how do i deal with my boyfriends rude children

You and your boyfriend need to sit down and write down the rules of your home, then meet with all the kids and lay out the rules and what the consequences will be.  Make sure you do not say your children don't behave say... Honey with the baby coming I would really like to make sure we are on the same page with the rules of the house can we sit down and figure out what we each expect of the kids.  Honestly if you were say to me you never see how bad your nephew behaves I would be mad too even though I know my nephew does not always behave the way he should.  After you have figured out the expectations and discussed it with the kids consistency will be paramount without it the kids will just ignore the new rules