Spot on, Atenco. I cannot imagine ever doing such a thing to my parents, Atenco. Sure I grew up there, in the house that they're still able to live in, but I did not pay the mortgage and bills on the place and still do not. I still visit, because I live abroad, with my children, for one month out of the year. Of course they would never take money even though I have offered that, but when there I do not expect to flout what I know are their rules, or for them to run round after me like a skivvy. I would never announce, 'Oh, I'm moving back in with you, to save money,' with no real goal in mind. Or cut them off if they said no.
They were married for 8 years before I came along. They are married still. They have busy social lives and lives, even when we are there, of course! And they are old enough to be retired. Thankfully, their retirement is comfortable, but it's theirs. They worked very, very hard for it together. They made many sacrifices in their lives for that. It's for them to enjoy. I did nothing to earn it but have benefited from what they did.
But I was brought up not to rip the piss out of people so I'd not dream of doing it to my parents, either. Or expect other people to pay for my house deposit by announcing that I expect to live with them.
He is 24, not 18, he has been living away for some time. The OP has stated he is one to flout the rules to get his way, and their relationship has been better now he is living on his own.
That's how you bring up people to be self-sufficient and not expect others to carry them through life.
They absolutely have the right to live in their home how they see fit.