Am I wrong for how I treated my children?

My ex and I got divorced a long time ago and have not remarried as we have been focusing on working. Our twin children have lived with me and my parents after that.

But the way my parents and I treat them is probably too strict, which leaves them unsatisfied with a growing hatred towards us. They moved to my ex-wife’s place as soon as they turned 18, regardless of how my parents and I begged them to stay with us.

I think the relationship between our kids and us started to worsen when my mother sold their pet dog and threw the newborn puppies away when the kids were at school a long time ago.

Although she explained that she did so out of her intention to get them more focused on their study, that still served as an event that wholly changed my children’s personality.

Still, things went beyond my imagination when my parents got into an argument with my kids as they recently went to my ex-wife’s house to convince the kids to return. The kids even physically attacked and swore at my parents.

They said they rejected the relationship between them and my parents and would not even attend their funeral in the future. They also said they had to put up with us since they were children, and now that they turned 18 already, they would not have to do so anymore.

My ex-wife supported them. She has also achieved strong financial capability, so objectively speaking, she can take good care of them now.

But I wonder why our relationship became like this. I agree that my parents were too strict, but they did so out of their good intentions. I couldn’t imagine that my kids would take it this seriously.

I’m puzzled and do not know what to do now that my parents feel sad and my children are treating us coldly.

What should I do?