Borrowed and lent on interest

A relative on mine needed a mortgage, but the bank wouldn’t approve the loan. So, in order to help him, I took out a mortgage from the bank, and lent him the money. We agreed that he pays me everything that I have to pay to the bank, but I am not charging him any additional interest. When I received my loan from the bank, we filed a heiter iska (a document that turns a loan into an investment, thus allowing to lender to charge an interest). And now I’m thinking that maybe we have to sign another heiter iska between me and my relative.  

Dear …!

Indeed, there are two interest-bearing loans here, the loan that you took from the bank and the loan that your relative received from you; you need to sign a heiter iska for both loans. So, you have to sign an heiter iska with your relative.

The best way to handle this situation (from halachic point of view) is that this relative of yours who borrowed money from you give you some object (sudar) that he owns, and that you acquire this object and together with this, also acquire a part of his apartment whose value is equal the amount money that you lent him.