There have been similar threads and most on here would say DC is an adult of course they should pay/do their own washing cooking etc However I’m in a similar position to you where I have adult dc and younger ones, and In my experience it’s not practical and adult DC are still part of the family and not a lodger. In my case, it does not work for me to do a wash load and pick out and leave adult DC things in order for them to do a separate wash later, this means extra wash load.
The same goes for meals, im not going to cook a family meal and leave the adult DC to sort themselves out. This seems wasteful and petty and what are you actually going to teach them? That they are only responsible for themselves and no one else?
‘That’s not my plate, I’m not washing it’, and I’m not folding those T-shirts as they are not mine?’
‘who ate my tomato that I bought for my sandwich??
I’d rather have us all support and help each other when needed. This I mean l(and it’s a process) teaching they adult DC to be aware of what needs to be done and stepping in when it needs doing. So if I’m home I’ll cook and load a wash if everyone else is at work but when they are back they can do other bits like wash dishes, Iron, hoover, clean garden, windows etc and cook when they are off etc
As for money I don’t think it’s unfair to ask for contributions towards household costs, show them all your expenses for a month to put things into perspective, and then come up with an agreed amount.
It might be trial and error to find what works for you, and there are benefits to having older DC, they take them out sometimes too xxx