Gawd, that is SO selfish. I felt uncomfortable sleeping in the adjoining room to my dad and HIS girlfriend (who turned out to be his wife without my knowing for a while....).
There were so many different ways to sort out that sleeping arrangement. Why couldn't HER son have slept in their room and YOUR daughter slept with her brother? Or even the girlfriend and her son in one room and your kids with their dad?? At least they would've got some alone time with him without her.
Maybe you should sit down with your kids (maybe with ice-cream or something equally as yummy/a treat
) and ask them how the holiday went/how they felt. Ask them how they feel about their dad and if they're getting on with him/the new girlfriend. At least that would give them the opportunity to raise any issues they have.
Tell them that if they ever have any problems/worries they'd like you to discuss with their dad you'd be happy to, just to know that they're happy. Reassure them that you won't make it seem like a personal thing coming from them, that you'll just tell their dad you've heard them talking about such and such and that you're worried that he's making THEM feel bad/uncomfortable.
Not wanting to tell you how to raise your kids or anything, you sound like a great mum, this is just what I'd have wanted my mum to say to me when I was still in an awkward position with my step-mum and was scared to say anything to my dad.
-Instead of telling me what a bitch my dad's new girlfriend was and what a dickhead he was. That really spoiled my relationship with both of them.