if I were you, I would seek the advice of a solicitor or the Citizens Advice Bureau
I am involved in trying to settle the estate of my late sister who lived in a house, the equity of which is shared between herself and a housing association. It is a nightmare - the agreement she signed was a death trap. I am not assuming you might run into the same sort of problems, but it makes sense to make sure any agreement is fireproof to the benefit of both of you
Mike