Any older folks with disabilities out there?

I'm the caregiver for my older brother (65, w/diabetes, plus mild-moderate dementia from hydrocephalus as well as COPD, and schizoaffective & bipolar disorders).
I joined us up to MFP to see if I could at least get a handle on his diabetes through diet, since getting him to do ANYthing other than watch TV was a struggle. I took him to visit a dietician for advice (which was more or less just "50% of his calories should be from carbs". Gee, ya' think? ) and a recommendation for target calories/day (he weighed 217 at the time).
We didn't see much progress though, until I used a TDEE calculator to figure out his actual caloric needs (as in, what he needed to have even if he was in a coma. No exaggeration: during this phase, the only activity he got during the day was walking REALLY slowly from the living room to the bathroom and back).
In the first month, I structured his meals around that figure, to get us both used to the idea. I plugged in the 50% from carbs here on MFP as a goal, and chose 25% protein since that's recommended for the elderly to prevent muscle loss.
As far as exercise, I got the VA (he's a vet) to schedule a stint with a PT. She was great, really motivating him to get on board with the idea of exercising.
Now his day is structured around what he CAN do. We 'walk the plank' (3 trips up and down his 60' wheelchair ramp) 2x/day morning and evening, weather permitting. Every other day, we do a 30-minute session of strengthening exercises (3 sets of 25 reps of multi-muscle exercises, currently: modified 'squats', where he stands up and sits down in a slightly-higher-than-standard chair; elastic band stretches to target his back, core, and rotator muscles; and finally arm circles to strengthen his biceps, triceps, and shoulders) then later in the day he rides his recumbent bike for 30 mins. Alternate days he does two 30-minute bike rides, so his muscles can recover from strength-training.
He 'earns back' half of the calories he burns in exercise in the form of treats. It's amazing what the promise of a cookie can do to get him past reluctance! (And no, I don't feel bad about bribing him. Whatever works! )
Since we started in Feb. '19, he's lost 35 lbs and gained 2.5 inches in his thighs, but more importantly, he's dropped his NPH insulin from 25 units at night and 30 in the morning, down to 8 units at night and 15 in the morning. I have hope that we'll be able to stop altogether someday.

I wish I could recommend something more concrete for you, other than figure out what YOU can do without it being painful, do it every day spread throughout the day, push yourself in tiny but regular increments to do more so you feel like you're progressing, and find a way to reward yourself (it doesn't have to be cookies. It could be a monthly massage, a night out, a new outfit, whatever makes you glow!)