Did the Sunnis believe that all caliphs should be descendants of Muhammad's son-in-lawAli?

No, Sunnis do not believe that all caliphs should be descendants of Ali, Muhammad's son-in-law. Instead, Sunnis maintain that the caliph can be chosen from among the Muslim community as a leader, emphasizing consensus and community approval. This belief contrasts with Shia Islam, which holds that leadership should remain within the family of the Prophet, specifically through Ali and his descendants.