Sects

Not all of the names you mentioned in your question had really claimed Imamate,but it is a fact that some of the children or grandchildren of curtain imams did wrongly claim Imamate.The reasons behind that were mostly political and for gaining worldly benefits. All those who wrongly claimed Imamate had failed,despite the political and financial support from the rulers and governments of their times who were always interested and keen to create dispute between the followers of Ahlulbayt. Being a son or a grandson of the Infallible Imam does not mean that he is also an Infallible,we read in Quran how one of the sons of prophet Adam [AS] did kill his own brother. Al-madeena [5]. We also read in Quran about the son of prophet Noah who disobeyed Allah and his father.Hud[45]. It is worth mentioning that most of those sons of grand sons who did wrong have repented their mistakes.

wasalam.

Every Muslim is responsible to obey Allah The Exalted and follow the Prophet SAWA. We are not allowed to blindly follow our families, culture, society in matters of faith without evidence. When the Muslim establishes concrete evidence that he is working according to the orders of Allah The Exalted, from Quran and according to the authentic orders of the Prophet of Islam SAWA, then he does not need to go through the different sects. We read in the books of Hadeeth that the Muslim Ummah will be divided into 73 sects, out of which just one sect will go straight to Paradise. The 72 sects which remain also had many sub sects over the many past centuries.A Muslim is not responsible to go through all the sects and sub sects as far as he has established authentic and concrete evidence that he is following the clear orders of the Prophet of Islam SAWA which was to keep following the Quran and Ahlulbayt AS.

Wassalam 

Shia Muslims are the real followers of the authentic teachings of the Prophet Muhammad (SAWA) and they will be going with him where ever he goes. The Prophet himself called his most pious followers as Shia of Ali as you see many Sunni books like:1. Shawaahid Al-Tanzeel by al-Hasakaani, V. 2, P. 66.

2. Al-Durr Al-Manthour by al-Siyooti, V.6, P. 379.

3. Yanabee' al-Mawaddah by al-Qandouzi Al-Hanafi, P.62.

4. Al-Manaaqib by al-Khawarizmi , P. 187.

5. Al-Sawa'iq al-Mohriqa by Ibn Hajar , P. 96.

6. Tafseer Al-Tabari, V.3, P. 146.

7. Tathkirat Al-Khawaass by Ibn Al-Jawzi, P.18.

8. Fat-h al-Qadeer by al-Shawkani, V.5, P.477.

and many other Sunni books.

Wassalam.

The Hadeeth which is narrated in Shia and Sunni books is (My Ummah will be divided in to seventy three sects). The additional words which you quoted are not authentic. Obviously, the followers of the Quran and the Progeny of the Prophet (SAWA) will be saved because they are the real followers of the Prophet (SAWA).

Wassalam.

1. Both Shia and Sunni scholars emphasised on the authenticity of all the narrators of every Hadeeth, but they differ when they come across some narrators who are controversial e.g. Abu Huraira, Samarah Ibn Jundob, etc who are considered as accepted by many Sunnis while not accepted by Shia scholars because of their behaviour against Ahlul Bayt(AS).
2. Shia scholars follow the most strict procedure of authentication of every narrator whether Shia or Sunni.

3. Shia scholars take Ahlul Bayt as the main source of the authentic Hadeeths from the Prophet (SAWA) not only because they are the most pious and most knowledgeable about the Real Sunnah of the Prophet (SAWA) as they lived with him, but also because of the order of the Prophet (SAWA) to all Muslims to keep following Quran and Ahlul Bayt (SAWA) (Saheeh Muslim, Hadeeth number 4425, and Tirmithi; Hadeeth number 3718 and 3720, and al-Mustadrak by Al-Haakim al-Nisabori; Hadeeth number 4576 and hundreds of other Sunni and Shia books.
4. Shia scholars have written the Hadeeths right from the time of Prophet Muhammad (SAWA) and through the times of all the Infallible Imams (AS), while Sunni scholars were forbidden by their rulers from writing any Prophetic Hadeeth from the time of Saqeefa till the time of Umar ibn Abdul Azeez who was first Sunni ruler who lifted tha ban on writing Hadeeths, which means that Sunni scholars did not write Hadeeths for around hundred years. That has definitely affected the authenticity and the accuracy of their narrations.

5. Sunni rulers used to interfere in religion to suit their political aims. Mu'awiyah for example used to pay huge amounts of money to some narrators to fabricate narrations in his favour and against Ahlul Bayt (AS). He used to kill or torture scholars who narrate any Hadeeth in favour of Imam Ali (AS). This corruption went on during tyrant governments of Bani Umayyad and Bani Abbas. Shia Hadeeths since beginning till now are pure from any political corruption.

6. Shia scholars following the teachings of Ahlul Bayt(AS) do not accept any narration which contradicts Quran, while you find many Sunni scholars narrate narration which are clearly against Quranic verses and claim than authentic narration is accepted even if it contradicts a Quranic verse. For details you may see ( A review of the two Saheeh ( Bukhari and Muslim) by Shaikh Sadiq Najmi and ( (Quick look at the two Saheehs, by Shaikh Aasif Mohsini and many other books in this subject).

7. Many Sunni books narrated from open enemies of Ahlul Bayt and considered their narrations as authentic. Bukhari narrated from Imran Ibn Hattaan who used to praise Ibn Muljam, the murderer of Imam Ali (AS), and also from Uthman ibn Hareez who used to openly curse Imam Ali every day. This shows that some non trusted narrators have penetrated in some Sunni books and taken as trusted narrators. This has added to the difference between Muslims.

Wassalam.

There are many narrations in Sunni and Shia books regarding the 73 sects, but most of the narrations have additions which are not authentic especially what is in some Sunni books that the saved sect will be those who follow me and my companions ما أنا عليه وأصحابي. Leading Sunni Ulama stated that this narration is fabricated.

Our Shia Ulama narrated many narrations about the 73 sects as find in Bisharat Al-Mustafa narrated from Ameerul Mo'mineen (AS) which states that saved sect will be those who follow the real successor of the Prophet (SAWA).

This narration does not mean that all Muslim sects will be in hellfire except one sect, but means that there will be right sect despite of the different sects. The followers of the right sect will be saved because there have obeyed the orders of Allah (SWT) and the Prophet (SAWA).

Wassalam.

Such claims come from those who try to play mischief with the meanings of Quranic verses. Shia Islam is not a sect but the real following of the Prophet and his Progeny. Allah (SWT) has granted His prophet Ebrahim (AS) with the title of Shia in Quran (Sura Al-Saffaat: 83).وان من شيعته لابراهيم 

Allah (SWT) called the followers of the prophets as his Shia as we read when a follower of Moosa (AS) was in conflict with one of his enemy

هذا من شيعته وهذا من عدوه

فاستغاثه الذي من شيعته على الذي من عدوه (Sura Al-Qasas: 15).

Shia of Ali (AS) are the followers of Ali (AS) who are in fact the real followers of the Prophet Muhammad (SAWA). The most pious companions of the Prophet (SAWA) were called Shia of Ali like Salman, Abu Tharr, Ammar, Miqdad and others. That is why you find many Hadeeths in Sunni books from the Prophet praising the Shia and saying that they will be in Paradise (Al-Haafidh Al-Tabaraani in Al-Mu'jam Al-Kabeer 1:320) and (Al-Haythami in Majma' Al-Zawaa'id 9:131) and (Jawaahir Al-'qdain by al-Samhoodi 294) and (Kanz al-Ommal 12:104) and Al-Salihi al-Shaami in Sobol Al-Hoda Wal Rashaad 7:11).

There are also many Hadeeths in Sunni books that Shia of Ali are the best of all creatures.  In Tafseer al-Tabari 30:335 a Hadeeth narrated from the Prophet (SAWA) : Ali and his Shia are the best of all creatures.

Same Hadeeth ( Ali and his Shia are the best of all creatures) is also narrated by Al-Haakim Al-Hasakaani in Shawaahid Al-Tanzeel 2:353 and Soyooti in Al-Durr Al-Manthoor 6:376.

Wassalam.

Sunni sects are four:

1.  Hanafi Sunnis who follow Abu Hanifa Ibn No'maan  who was born on year 80 after Hijra, after 70 years of the passing away of the Prophet Muhammad (SAWA) and died on 150 after Hijra.

2. Shafi'ee Sunnis who follow Mohammad Ibn Edrees al-Shafi'ee who was born on year 150 after Hijra and passed away on 204 after Hijra.

3. Maliki Sunnis who follow Malik Ibn Anas who was born in 93 Hijri and passed away on 179 Hijri in Madinah.

4. Hanbali Sunnis who follow Ahmad Ibn Hanbal who was born in 164 Hijri and passed away on 241 Hijri.

Shia follow Ahlul Bayt who are Imam Ali, Fatimah, Imam Hasan, Imam Husain who lived with the Prophet Muhammad (SAWA). Then the 9 Imams from the kinship of Imam Husain (AS). 
Shia is not a sect but a title which is used in Quran for the sincere followers ( Sura Al-Saffaat 83 and Sura Al-Qassas 15). The Prophet Muhammad (SAWA) gave the title of Shia of Ali to the most pious of his companion and most obedient Muslims ( Tafseer Al-Tabari, V.30, P. 335) and Shawaahid al-Tanzeel by al-Hasakaani 2: 353 and Tafseer al-Dorr al- Manthour by Al-Soyouti 6:379.

Shia believe and follow the Prophetic order to all Muslims to keep following Quran and Ahlul Bayt (AS) to be andbremain on the Right Path. This Hadeeth is authentic and narrated in Saheeh Muslim 4425, and Tirmithi 3718 and 3720 and in many authentic Sunni books.

Shia follows the Prophetic Hadeeth that the successors of the Prophet will be twelve. (Saheeh al-Bukhari 6682, al-Tareekh al-Kabeer by Al-Bukhari 8:410), Saheeh Muslim 3393, 3394, 3395, 3396 and many other important Sunni books.

Shia believe that the Prophet Muhammad (SAWA) `did not leave the Muslim Ummah unguided regarding the divine leaders of Muslims after him, but he clearly informed the Ummah and asked them to give allegiance to Imam Ali (AS) being the first successor of the Prophet Muhammad (SAWA).

Shia Muslims follow the Prophetic Sunnah of the Prophet which is Been narrated by the most authentic source who are Ahlul Bayt (AS) and their pious followers.

The main difference between Shia and Sunni Muslims are in two issues: First : Who succeeds the Prophet in leading and guiding the Muslim Ummah?

Second: From where we should get the prophetic teachings ( Sunnah and Quranic meanings) after the Prophet Muhammad (SAWA).

Most of the tyrant governments like Bani Omayyah and Bani Abbas till today are against Shia Islam and played big role in defaming Shia Islam and spreading false propaganda against Shia.
Shia Muslims present evidence that they are following the original teachings of the Prophet (SAWA) not only from their books but also from the Sunni books and always call and practice dialogue.

You can find more details on this subject in many books written by ex Sunni scholars who reached to the reality of Shia Islam through scientific research like books of Dr Tijani and other scholars which can be seen in www.aqaid.com and www.al-Islam.org and many other websites.

Wassalam.