Could you share Sunni references indicating that the third caliph was related to Marwan, whom the Prophet expelled, and that he appointed them to leadership roles, resulting in his assassination for contradicting the Prophet's principles?
It is a known fact in books of history and Hadeeth that Marwan ibn al-Hakam was a cousin brother if Uthman ibn Affan. Famous Sunni scholar Al-Dhahabi mentioned this fact in his book (Siyar A'laam al-Nubalaa') 3:476 . There is no dispute between historians that Marwan ibn al-Hakam was cousin brother and son in law of Uthman ibn Affan.
Wassalam.