Unless your BF does something about it, it's not going to change. It's up to HIM to discipline his kids. I have 3 stepsons that used to run wild at my house, because their father allowed it, and their mother let them trash her house too. I put my foot down and refused to have them in my home until he decided to start being a father. And that IS YOUR HOME! It doesn't matter that you were the last to arrive, it's still your home. Don't back down. He's doing a real disservice to his children if he doesn't step up and stop this behavior. And those boys are plenty old enough to know better, too.
I'm sending you hugs, and hope that things get better
