I left my DC's dad about five years ago, because he only ever thought of himself, treated me as a servant (albeit usually a favourite servant 
) and was unable to give me any signs that he knew me at all or cared about me. After I left - to his credit - he stepped up and started taking some parental responsibility rather than leaving everything to me as had been the norm.
He has had them for a long weekend EOW and a night in-between, and that has been the setup for most of the time we've not been together. I worry about the DCs because I think he uses them to look good, and will make them feel to blame if anything goes wrong, rather than take responsibility asvthe adult in the situation. They often come back here overtired, crawling with headlice and having done no homework, piano practice etc because he's been dashing around seeing all his friends with them or taking them on fancy holidays. I tell myself it's not the end of the world, but it is annoying, particularly as he insists he wants to be involved in all aspects of family life.
Every now and then I worry that he's trying to take more control. Like this evening, when DS was supposed to be coming back here, according to the new arrangement. But XH just happened to be there at the end of school, so DS felt he had to go back to his house. He was supposed to come back in a friend's car, but the friend obviously didn't feel she could interfere, so she just hoped it was ok to leave DS with him, and presumably felt uncomfortable for being involved!
He's also suggested to DD that when she does GCSEs in a year, it'd be easier for her to be based in one house... oh, and he might buy a puppy about then. She reported all this to me - she thinks it sounds a great plan. Not surprising, she's his favourite and she won't hear the others say anything negative about him. He often leaves her to look after the younger ones, and that can annoy her, but she doesn't see it as a situation he's causing. I suppose he's pretty good at justifying what he does.
The DCs talk about the lovely food he cooks for them and I try not to get petty but it often feels like a popularity contest. I give them chores each day, only about 5 mins and they've not complained, but I worry that that influences their decisions about whose house to stay at, too.
Basically, they're old enough to decide whose house they want to go to. So, short of making sure I don't get no contact, is there anything I can do about little attempts like this to take more of their time?