Sounds like the lack of cleaning is more from lazy habits / lower standards, than you keep for yourself. From the description it seems like the disability is not a severly limiting physical factor preventing him from keeping a presumably small rental, clean +/or uncluttered in the past. He has 24 hrs a day to devote to his own pursuits - minus the doctor visits [?]
If you do follow this thru, i'd make sure the small house / mobile home / RV is Not on a rented lot , like a mobile home park. Keep the # of payouts that need to be made to a minimum, taxes and utilities only, no rental propane tanks or similar. If he would grant a power-of -attorney for his "bills" that you controlled, out of his SS benefits direct deposited account, that income money would only go as far as it had a positive balance. What stops him from getting to the bank on the day of $$ infusion, and pulling it out, before you pay the electric bill ?
Can you look at this as .... instead of getting your spouse a 2 yr old Lexus for $ 40K, or taking a few trips across the Earth for a similar cost , having a kitchen remodel in your own home, etc -- that you are willing to help him find a $ 40 K home on its own plot of land -- review the relevant paperwork youselves, or have an attorney or title firm review the contract if it is a private owner sale [ not MLS listed or represented by a RE agency ]. Then bring along the purchase price to closing / deposit it into an escrow account with title company -- and the house just goes into his name only,with zero mortgage owed, and you are not attached legally, except for vouching that you gifted him the money.
Then if he wants to have you control the payments to the county for taxes, and the power provider, great! - and if he doesn't want to sign over that autonomy on what day bills + taxes get paid + how much -- well you made an attempt and he'll have to deal with it himself , at his own peril, not yours.
Also -this way when you go visit , the probable future mess will not bother you as much.
Even this betrays that most people don't understand the pitfalls of providing housing for family.
As I said in my post, I was perfectly willing to have my contribution end up charity in the end.
It still caused an entire year of daily stress and put strain on my marriage, and it falling through was the best thing that could have ever happened to me.
The pitfalls come with trying to take responsibility for another adult persons living situation when that person is not a legal dependent.
There are invisible and unspoken relationship dynamics between everyone. We're rarely even conscious of them, but most relationships stay functional because we've all been pretty well programmed to stay in our lanes with respect to one another.
Buying a brother in law a house trounces all over those social norms, and violates all sorts of unspoken boundaries. This means that for everyone involved, the standard for communication and respect is much, much higher, because even the most casual of conversations are now at risk of causing feelings of disrespect and unmet needs.
It's not the practicalities that are the pitfalls, it's the interpersonal dynamics that are the risk. So you can cover your ass on the financial side down to the worst possible outcome, but it's impossible to predict the interpersonal fallout, because that's what happens when you don't play within the bounds of established, healthy interpersonal dynamics.
Fuck with the healthy order of human relationships and you risk serious consequences, no matter how careful you are.
OP: how would it make you feel if you offered to do this, and your brother in law was enormously grateful and said all the right things. Then when it came to looking for houses, he started being really picky about what you buy, started saying things like "of course I'm grateful, but this is my house, my life, I should get a say about where I live" when you start suggesting places to buy and he whines that they don't have a specific, not important feature that his current place has.
Would you be offended? Frustrated? Would you complain to your spouse that it doesn't make sense for him to complain because you are offering him something so much nicer than his current home, which he can't even afford?
I'm not saying that this is what will happen, I'm saying this is what CAN happen, very easily.
And what are the chances that you and your spouse are on the *exact same page* as to what is a step too far? What happens if one of you is pissed off and ready to bail on the whole thing and the other isn't?
What happens if you insist on calling it off because you've just been pushed too far, and your spouse grudgingly agrees, and then BIL gets evicted and is homeless? How does THAT get resolved? What does that do to your marriage?
Again, this is all just off the top of my head.
But all of this is not just possible, it's probable when you do things like this. Some version of what I described is LIKELY to happen.
And it's WAY MORE stressful than losing 40K.