Adult kids staying and not contributing.

My first thought was I’m glad my children don’t behave like that. Younger son ended up staying with us for a year during Covid. He did his share of cooking, cleaning and feeding the cats. But it’s probably too late now OP.

That is just taking the cake and the biscuit. But tbh is too late now, it would have been better to establish house rules in the beginning, asking them if they could shop and make dinner at least once a week and clean up after dinner if you have made it, also you should have shown them how household appliances work and told them to tidy up after themselves. All this could have been done in a lighthearted manner without being heavy handed. And when you went away you could have left them a list of jobs that would need doing without it seeming onerous.
Sorry this happened. But am afraid sometimes our adult children regress when at home with mum and dad and need reminding that they are now independent adults who should clean their own mess.

They will soon be gone. Surely you don't want them to go and there being a falling out? I would be disappointed too if my children did this but I would have other stronger feelings that they were going so far away and at my age I may never see them again.