It may be hard on you, but your aunt has a right to live her life as she chooses. She has accepted that she cannot manage at home and has agreed to go into care. However, she still has and owns the house and if she doesn't want to sell it - well, that is her decision.
What you need to spell out to her is the results of that decision. That the house will be empty and unvisited - her continuing to own the house does not mean that you have to care for it. It could be occupied by sqatters, the heating system could leak, if the heating is not on and there is a freeze, then pipes could burst, if it floods, no one will sort it out, if gales blew of roof tiles, they would remain off.
I think you need to make it clear to her that she can continue ownership, it is her right, but if she wants it looked after, fit for her to move back in (however unlikely this will be) it will need to be looked after and maintained, so she will need to employ a company of professional house watchers as no one in the family can do it.
There is more than one approach to a problem like this.