Ask A Question About Islam And Muslims

9 Questions

Denouncing wrong doings of responsible persons against the interest and rights of people is an Islamic duty in every Muslim. We need to be wise and careful not to cause harm to ourselves and other believers when we express our objections on the wrong doers. Amr BilMa’roof and Nahi ‘Anil Munkar is obligatory with its conditions.

Wassalam.

Bismihi ta'ala

Yes, if it is crucial information and would affect the success of the marriage, and you are asked for your input, you must be honest. 

This situation is among the cases where gheebah (backbiting) is permissible, or maybe could even be obligatory. 
Of course, you must be careful that it does not somehow backlash onto you as well. 

And Allah knows best

You must be sure that the person is really a malicious and there is risk on your friend from him. You can then hint to your friend to be careful before dealing with people. 
Wassalam.

Bad friends can harm you more than your enemies. Never indulge in wrong even if your friends do. You must be careful that your friends don't make you lose your pious character nor make you share their bad acts. 
Wassalam.