I agree with Dawn and Kevin..do more.

Simply put? Don’t use it? You lose it! And, most neuros somehow overlook that necessary NEED to get moving and using yourself!
Nerves have likely been damaged, or worse, and muscles are in approaching atrophy from lack of use. They must be used to regain circulation and motor control then aid in nerve regrowth to re-connect the rest of the incredible human ‘network’ that is in ourselves.
I hope and pray that you find super understanding and talented therapists to work for your Marshall! And not the ‘GungHO!’ sort that wants 50 reps off the top. ICK!
When I’ve had PT? I’ve found 2-3 times a week worked well for me, gave me time to ‘recover’ from the one day and get ready for the next? Also, be sure to ask if there are some sorts of home exercises that can be done safely and are ones a body can ‘build up on’ in terms of gaining strength. I’d found these helped me progress a lot faster? Because I didn’t have to ‘do’ them all at once? Just do say ten reps now, 15 later and on up. It’s also less boring?
With the PT? I found I got stronger as I went along w/the program? BUT…. when I was due for my IVIG? I was definitely LOW on energy, until the next infusion.
In the end? It’s got to be up to Marshall to decide if he’s too uncomfortable in the trying or the doing. There are lots of exercises that can be done just sitting that can build and strengthen muscles to the point where it’s less unpleasant. Work with the pros to get around it all and get some progress?
My heart is with you, I’ve CIDP, but I’ve been immobile a few times more than I have wanted to be. I don’t LIKE it one BIT. Sooo? Make it a new journey? One of progress, I truly hope for. Keep heart and don’t give up!