You have a lot of overlapping issues here, and I'm glad you asked as you have some very tough decisions to make, and it seems like you don't have a lot of time to make them all either. (due to being released from rehab)
I will try to answer everything, but please just ask again or for more detail if I don't cover enough, though I'm feeling this could be a long post anyway.
Firstly, yes, Chris stayed here with me right through and died very peacefully at home.
I must stress that this was my prime goal, so all my decisions were made in light of that. This does not mean that things I did are set in stone as the right way to do anything.
We had no stairs, so that was a bonus, because Chris refused to attempt to be safe and we had some terrible injuries from falls.
Even though we had no stairs, for a lot of the time Chris only lived in half of the house as he either couldn't get to some parts, or even if he could it was too exhausting (it would take 15 minutes to walk through 2 rooms to get to the toilet with walker, yet he insisted he wanted to do this).
I set up the lounge room for him and removed all the furniture from there except the TV. He lived either in the lounge room, or on the back verandah.
In the lounge room he had his riser-recliner chair and hospital bed. On the verandah he had a chair that MND NSW lent us that he was able to use right through.
Our health setup in Australia is very different. Actually it has changed a lot even since Chris passed and I shudder to think of caring for him now with the cut backs and changes. But at the time Chris was awarded a disability pension and I was awarded a carer pension. This was not enough money to live on, but it also gave us access to other services either free or for very low cost.
I was able to finish up most of my 'away from home' work in the first 6 months while Chris was still reasonably mobile and could do some things for himself. I work in my own business. I continued trying to do the kind of work I do from home, but it was incredibly hard as my work needed me to concentrate for decent periods of time, and even when help was here he was demanding. But I waffled along doing some work as I could, and at least I could stop and start and work early in the morning (like 5am) or later in the evening if needed.
We had help staff coming in on weekdays for different lengths of time each day. I only really went out if one of them were here. Occasionally in desperation I would duck out to shop for an hour with Chris settled in his recliner and promising he would not attempt to get up, and no equipment in the room for him to even consider.
I am on 14 acres, so I was also trying to keep up some of the things here, but I had to just let a lot of it go. There's actually a lovely 'after story' about what nature did to heal me and the land as a result, but that's another tale.
So yes, she is going to need 24 hour care/assistance, probably now.
You say you have a relative that could move in with her? So could the lower level of her house be set up? Forget about what the rooms are currently supposed to be. Yes my house looked more like a hospital than a house, but it looked more like a home than any hospital could!
If that relative could do that, could you then set up a roster so that this relative gets some time off, as this will be really important. Maybe your husband could stay one night a week, or spend one day a week there, or you both go over a few evenings or every second weekend or something and give her/him time off?
Or could you get someone to come in and do housework, the shopping or other chores. Could you set up a meal roster through family or other friends?
Could you get hospice in the home involved maybe?
This disease requires us to start thinking 'outside the box'.
I was pretty much alone with my role as CALS. Chris's adult children wanted to bury their heads and stay away as it was 'too upsetting'. So it was me and the health and care team I was able to build, and it was tough. But it was all choices, I chose to have him at home, living and dying with dignity, and though no choices were easy I did find the combination that worked to achieve my goals.
So maybe you first need to get all involved parties together and have a discussion on what are the goals for your MIL. Then start looking for solutions that will achieve those goals?
A goal like - I want to stay in my own home is valid. But can you meet that goal? Maybe you can with some collaboration between family, friends and hired services. If not, what can you achieve that is the closest and prevents her from going into a nursing home?
Now the really hard bit is that with FTD, she can't articulate any real strategies that will suit her to meet the goals. She can know what she wants, but it takes executive function and empathy to put a good strategy in place. So the conversation may be best only being goal setting with her. Then you may all have to hold your own team meetings to work out strategies and only go back to her with options that you have discovered will work. She won't be able to wade through possibilities and ideas and keep up with which are going to be put in place and which ones didn't work out to be workable choices.
This is your thread now, so use it bounce as much as you need to off me, and others that may join in to help out.
I also have a slight concern when you say she is in a rehab unit - I hope they understand ALS and don't push her physical limits.