OP, make a list of everything you do every day, and what it would cost your husband if you weren’t there, and show him. He should be putting his hand in his pocket wherever he can to contribute to the household, e.g. paying for a cleaner.
It also sounds like if you could just get either drop offs or pick ups done, you would have a bit extra time. I know you have trust issues from childminders, but your kids are older now and hundreds of thousands of kids go to childminders without issue every day. If you could get someone to do one of the school runs, that would give you an extra 90 minutes per day. Or if you could hire a helper, you could get some work done in the house while the kids are present. Maybe not cleaning or tidying, but definitely life admin!
If you truly enjoy your volunteering, don’t give it up, as it’s your one bit of identity outside being a mother and you should treasure that. But ask yourself if you really enjoy it, or if you don’t want to let others down. If it’s the latter, you have to stop and take that extra 7.5 hours for yourself as you are drowning.
I’m an adult with Asperger’s and ADHD, and I still have terrible sleep problems and nocturnalism. I read yesterday that cortisol release in autism is abnormal or completely reversed, causing morning drowsiness and poor motivation, and preventing sleep at night. The only cure is apparently cardio exercise - so maybe you could try this for your SEN kid somehow? Maybe get a little indoor trampoline or something?