So... You don't like her boyfriend, you don't like that she goes to parties when her kids are away, and you don't like that the kids spend a lot of time with their father?.... Also they don't have a set sleep schedule? This is why you're cutting a 14 year friendship?

Your friend has been through hell of a lot. She's had twins very young, she's become a single mother, and it sounds like her relationship was pretty rough on her. She still managed to hold a job and provide for her kids. You should be proud of her for her strength and sacrifices.

If she's stressed and needs a night out, there is NOTHING wrong with leaving the kids with their own father. Your low opinion of him means nothing. He is their father. Even her low opinion of him means nothing. He is their father. If they were being mistreated it would be a different story, but they aren't, and it seems like they are a positive influence in his life - that he enjoys having them. If it's not a source of stress on their relationship, the kids will benefit enormously from having both parents being very active in their lives.

He is not your father. Everyone has their problems and his problems with alcohol does not explicitly mean that he is a shit person who will definitely abuse his children. I'm sorry for what you've experienced, but yes, you are projecting. You haven't listed any signs of mistreatment in your post. Their custody arrangement and sleep schedule is not mistreatment.

Thee issues you have with your friend are because of your own issues. If you leave, leave because she's not kept up contact, there's no reason to bring her children into an argument, it's unnecessary and low.