All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Your relative should know that it is impermissible to take a usurious loan to own a home as long as he is able to rent a house.
If renting is not possible and it incurs unbearable hardship, and this hardship can only be removed by the usurious loan. In that case, it is permissible to take a loan on the basis that necessities permit the prohibitions.
As for what you intend to do, if your relative takes the prohibited loan, and you want to reduce the amount of the loan and the interest on it, then that is permissible.
Allah knows best.