I texted ds and asked him directly if it bothered him at all to stay in a different space. He texted back (with an ! - always a positive sign from the young folks) that he is not bothered by that at all. It is easier and less expensive to stash him somewhere than mil since he will be here fewer days. Also less expensive than renting a larger place for all of us. I’m going to have to get over the “sleeping under the same roof” thing.
If mil says anything at all about being relegated to the sleeper sofa while ds gets a real bed (she didn’t last year when he stayed at friends’ condo), I will allow that to open the door to a conversation about future years and what might be more comfortable to her. I really don’t think we should be expected to pay for her to stay somewhere else if she doesn’t stay with us. She’s not a poor person.
Thanks to everyone for thoughts, support, experiences, and ideas. I tend to fixate on things and make them bigger deals than they are. Ds wil spend all his non-working time with us in our place and just sleep elsewhere at night.