My Dad (88) has become very combative. Any advice?

He recently has gotten divorced from his second wife. He has always been very opinionated. My older brother seems to have the hardest time. I feel as though he is the one who is always challenging my father. Sometimes I just let my father say what he wants to say. My younger brother chooses not to call him much. I talk to my dad every few days. My older brother talks with him everyday.my older brother lives in the same city as my father. My younger brother and myself live across country from my father. We are 51 I am 56 and my older brother is 59. Looking for articles or suggestions