I think the answer here if I was faced with this problem would be to remortgage to clear my relative and clear as much unsecured borrowing as possible!
Talk to a financial adviser about how much you can borrow. Your difficult relative would most probably want his money back.
Failing that is it possible to sell and find somewhere else to buy?
Do agree about the credit cards and borrowing and please learn something from me. Credit is a financial cancer it just grows!
You can now get a very good Mastercard where you pay money into and you can use like a credit card and their site is :-
www.mycashplus.co.uk
It is very good and you only have a small monthly charge and a very small initial fee.
With your personal bank account please ask them to remove your large overdraft and perhaps just have a £250 limit on it.
But please promise us that you will cut up those nasty credit cards!
Regards
Ray