Easter Holidays

Yesterday was a rough day. We had Easter dinner at my parents.  My dad and I had several disagreements mostly about my kids. He usually keeps his mouth shut even though I know he thinks they are badly behaved at times and doesn't really understand.  My  oldest was calling my youngest a loser so my dad said well your a loser then because your his brother.  I told him u shouldn't call ur grandson a loser. He said well, he shouldn't call his brother a loser. I said well, siblings do those kind of things.  Me and my brother did. He said not while he was around. He then made a comment about my kids never listening to me.  I said well, we didn't always listen to mom but that didnt reflect on her parenting. He said I don't want to talk about it. Fine by me! Later... My oldest called his brother the b word.  I sent him for a time out and he yelled and ranted and raved but did go for one.  My dad says why does he have to do that?  in a disbelieving tone.  I said probably because of his autism. Good thing he didn't say anything else cuz I was in no mood between disciplining my son and his comments. Later I had invited a friend over that has known my parents and I for many years. We were having a discussion about my friends  boyfriends stepson. Long story short because I don't really have her permission he said your not my real dad, I dont have to listen to you.  My dad said he should have responded then I don't have to drive you places, buy u things, do things for u etc.  My friend and I both disagreed and said that would just start an argument. My dad said it would make him grateful for the things the step dad did for him. I seem to remember times when I didnt want to do what I was told and my dad would respond by saying then I don't have to drive you anywhere or do things for u and that would make me just think he didn't care.   Of coarse I didnt think to say that. In the end of that convo I just ended up saying Its pointless to argue and my dad of coarse had to have the last word saying I think I have learned something in my ____years. Funny cuz I could have sworn my mom did most of the parenting unless we were really in trouble. What approach do u think would work if a child says your not my real parent?