sorry, your MIL wants her adult son to be "taken in" by a relative when she's gone?
Yep, she certainly does. First she tried the 'Who will look after BIL when I'm gone?' Now she does the sighs. If we're in town for something, she'll say, 'Oh, I can't meet then, I have to take BIL to the JobCentre' (he dips in and out of work, and despite living in a city with loads of good public transport and their living a quarter of a mile tops from the bus stop, he simply cannot be expected to catch a bus that travels straight down the road to the JobCentre.
He sits on the sofa in the lounge and expects to have cups of tea handed to him and taken away. He won't even bother himself to microwave a ready meal or make himself a sandwich.
He's in his early 40s and has no health issues.
But he won't come visit us out here because a) we don't offer to go through and ferry him over and b) DH expects him to prepare his own meals, cups of tea, wash his own dishes and muck in with the work.
I made it very clear to DH that if he even sniffs of moving him here once their mother dies, she's nearly 80 and has tons of medical problems, then it's divorce for us and I'd say the same if it were my own brother or sister, I really would.
I already have an autistic son who is very stubborn and showing definite PDA traits, over my dead body will I take in an able-bodied adult to sit on the settee all day and expect maid service.
I think the idea of your DH's taking time off work and going and staying with his dad a month or two is a very very good one.