I'm a single parent to two SEN children, not quite the same situation but based on your 'D'H attitude, you may as well be single.
In my LA children with additional needs can be signed up to the HAF program, even if not on free school meals. A lot won't be suitable but ours has a few SEN specific activities that I use as restbite (there's one forest school and one SEN play centre based one that DS will stay at, so I've managed 4 days 'off')
Are there any SEN groups in your area? We're lucky where we are that we have a few different organisations (mostly charities or parent lead groups, not SS). It definitely helps.
For today, its ok to have a messy house and order takeaway. Longer term, you need to find ways to reduce your load, as doing everything just isn't sustainable.
For me, that looks like prepared frozen veg & oven food more often, basic joggers/leggins & t-shirts all round, that get washed together with no separateing or ironing. Enclosed garden, so kids can still burn off energy without having to be taken out every time. And most importantly, melatonin. If you haven't already talk to your pediatrician about a prescription. Getting a good night sleep was definitely a game changer for all of us.