I am not a legal expert by any means
But.
He is trying to claim he was financially dependent on your Aunt.
However, he agreed to pay rent on a property that you own, meaning he wasn’t financially dependent on her for housing. He was simply a tenant and you are his landlord.
He also paid the bills there. So he wasn’t financially dependent on your aunt for those.
And she wasn’t his carer.
They didn’t live in the property together and were not spouses/married.
So on the surface, he wasn’t financially dependent on her for anything. Which from my understanding is the basic legal definition of a dependent. Someone (usually a relative or spouse) who relies on someone else for financial support and care.
He just moved into a property as a tenant. Didn’t pay the rent, but paid the bills. And now he is being evicted by the landlord (you) as the house is going up for sale.
I don’t see how he can think that, legally, he has a case!
Seems more to me he’s just trying to drag things out so he can live there longer.