It’s sad all around.

But trying to convince your son to stop seeing his son (even if he’s not biologically his) doesn’t sound right to me. Your son is a grown man and it sounds like he has his own place and that’s where he sees the kids. If they misbehave, they do so in his house, not yours. The aren’t even visiting your house

You said mom doesn’t want children in your house. I wonder why. She is ok with kids being with dad in dad house, just not in grandmas house. What led to that decision? It sounds that there is animosity between you and the mother of the boys.

Regardless of moral or legal components, unless your son is incapacitated and you are his legal guardian I don’t believe you can or should convince him to do something you think is right. You might be in danger losing your son if you push him to live his life by your rules.

I know it’s hard to watch adult kids making decisions that might differ from how you do things. But that’s part of raising kids. They grow up and make their own mistakes