Oh. My. God.
I would go stark staring bonkers living like that!
My DC's all muck in. And if my Ex eats here (usually three times a fortnight), then he washes up.
My DC's all help with chores, and as for your lazy arse husband, I would (and did, hence him now being the Ex) LTB.
Just down tools where your tool husband is concerned. And probably where your 15yo is concerned too. Both ate capable of working a washing machine, putting clothes on a line, folding and hanging clothes, cooking themselves a meal, and washing up after.
Buy them both their own set if student cookware (they do basic but full sets from tin opener to plates, pans and cutlery).
Give them their 'share' of the food money each week.
And PADLOCK all the other cupboards.
If they don't clean up behind themselves, put any of their mess on their bed / your husband's side of the bed.
You will still have to cook for the two little ones, but even they are more than capable of helping with jobs - especially the 7yo. My 2yo with SN's can wipe the table and dust! (Badly, but he tries!)
Clothes not in basket? Don't get washed. I haven't washed a single item of clothing for ANYONE in my house that isn't in my washing basket, since they were 4yo.
They run out of pants? They will have to wear dirty ones for a day, and hurry up with putting their dirty ones in the basket!
They don't food shop and buy themselves food? They will get very hungry, very quickly. If all the food for you and the LO's is padlocked (yes, you can get padlocks for fridges and freezers, SN suppliers sell them), then they will have no access to food other than the SHOP and COOKER.
Seriously, you will drive yourself into an early grave chasing after them all like this. So just STOP.
Just STOP. You are not a doormat.