OP, why is his living situation not suitable for children? Is this something he can change?
From the sound of it, you would be fine with him seeing the dc more (as long as in a suitable place), and they want to see him more, and he knows this, but isn’t stepping up? It’s difficult, but as you’ve already realised, there’s not much you can do about it.
my exH insists he is a hands on involved dad. He sees them (theoretically) EOW and one night in the week. Eldest and middle dc don’t go at all, so see him high days and holidays only - they are due at his this Christmas, and out of the weeks’ contact they both want to go for Christmas lunch and a couple of hours after. Youngest dc still goes, but not always the full allocation of time. In reality, he has no idea of what is going on in their lives, cannot name friends or teachers at school, and doesn’t even know what year they are in at school so can’t find relevant events on school calendar etc. The kind of parent he is in his head, and when talking to his friends and family, bears little resemblance to the actual parent he is.
how old are your dc? It might be that you are going to need to start helping them through some very difficult emotions, as they may be starting to see/realise that their dad’s interest in them only goes so far, and that is a hard thing to come to terms with.