I do see all sides of this story as I have been in this situation. The difference was I was a FRIEND and not family.
I agreed to let a mate move into my spare room when his relationship broke down. I lived alone and had the space. His parents were abroad having retired there and other family and friends didn’t have the space. It was agreed that it would be for a maximum of 6 months while he got on his feet and found somewhere else to go. He left the family home despite her being the one to cheat because he cared about his kids.
I never thought about the kids when I agreed and how he would manage go parenting and spending time with them. I only envisioned having him as a roommate.
within 4 weeks I was regretting my decision not because of the kids but because I valued my own space and didn’t realise how much until it was too late.
He would have the kids stay (he did ask first) and I agreed as well he is a father and should be responsible for them and I believe fathers should be just as involved as the mothers. My house was busy, kids stuff everywhere and my peace and space was gone.
I sucked it up as I had made an agreement and knew it was only going to be for a short period of time. He would take the kids out and do things and I would make plans to be out too. Then we would have time together at home.
it wasn’t an ideal situation, he knew this, I knew this and so did the kids most likely (sleeping on camping beds) but I made it work because I cared enough about him and the kids.
when the time came for him to leave I was relieved and was looking forward to the house to myself again. Turns out I missed having the kids around and the mess that went with it.
The way I see it is if I can help then I will. I think the issue OP is you haven’t given consideration into the whole picture. Just thought you would help your son out and now the reality has set in your not liking it. speak to your son and ask about him finding a home for himself. Ask if you can help in any way with that and set a deadline for him moving out. Don’t force it and certainly don’t try to cut his time with DD (she doesn’t deserve it and quite frankly dad should be involved and 2 days one night isn’t all that much). In the meantime suck it up and learn to live with it. Otherwise if you force him to move in too short a time or push him to abandon his daughter then you risk losing him and her
would I do it again 100% yes as I feel good knowing I made a difference but I would have a long hard think and chat about what was expected from the guest (kids/pets/sleepoevrs). To me friends are family and if you can’t help out those closest to you when they are having a hard time then you will lead a sad and lonely life.