How do you talk to your children about their relationship with their other parent? Or just don’t?

My son is 11 and I have been separated from his dad since he was 2. His dad isn’t involved in his life when he isn’t there. He doesn’t do school events, sports, drs, etc even if it’s in his time, I get him and bring him back if he wants to go. He has me, his step dad and two brothers in this house hold and at his dads he has him, his step mom and 2 brothers. Recently he has been having some issues at his dads (he goes every other weekend). The problem is that there is a lot of fighting, his dad has some anger issues that he doesn’t work out. The last time he was there his dad called his older brother a d*ck infront of his girlfriend (he’s 16), so he yelled back and his dad told him that he wanted to hit him. This really bothered my son amd then there was fighting with his dad and step mom. When he got home his friend came over, who is also in the same scenario that he visits his dad every other weekend. After my sons game, I asked if he wanted to call his dad and he said, “no, he’s mean”

His friend, “mine is mean too”

Son, “I be mine is meaner”

Friend, “no”

Son, “does yours cuss at you all the time?”

I didn’t know how to react to what he said or how to handle for the situation. Any advice? Thank you! Sorry it’s so long!