Hi @1983 and welcome to SANE,
It sounds like you are in an extremely exhausting situation, all 3 kids I have living a home have complex needs. My 24yo has PDA ( Pathological Demand Avoidance), Agoraphobia, ASD, ADHD mixed, severe anxiety. Without knowing your son, what he is diagnosed with, it is hard to help. I know with my 24yo, one day they woke up and it was like things started to click, things they couldn't do a few days before, they could that day. But I have also found that things that they had done for years, had gone, regressed.
Have you though of a psychologist for your son or for you to talk to about the situation? someone for you to vent to and give you knowledge, ideas of what could help your family.
Before my child was Diagnosed with PDA and Agoraphobia, waking them up of a morning was hard. I never knew what reaction I was going to get from them, some mornings they would set up in bed with a fist raised. This I learned later was because of their diagnoses and they didn't even know they were reacting this was, it was an automatic reaction, anxiety over leaving the house and their brain wouldn't let them. ( sorry I'm not sure if I'm explaining this properly)
In the end it was a psychologist that diagnosed and explained and worked with me to help them ( they refused to engage a lot of the time). Now I have a 24yo that can leave the house more often ( I'm mean and make them walk to the shop to buy their own smokes) but they can somewhat function now and started last year cleaning their own things.
As for self-care there is an app called Goblin Tools. It can break down tasks to smaller more manageable steps. It is great for people with ASD, ADHD and more.
Please know I'm sending virtual hugs, I know how hard this can be and you are doing a wonderful job.