1) If someone wants to build home and they do not have enough money and want to take loan from a relative who have saved money in bank (islamic banking system)on which they receive interest, are there any issues using this money for making home?

2) If someone gives u a gift eg a suit etc and its from interest money, since interest is haram in islam (islamic banking)and the person receiving gift also knows that this money is from interest money, can they offer prayers wearing that suit or it is haram? What should one do in such case?

1- No issues.
2- Yes, you can, because
a) You cannot guarantee that the money is purely from interest.
b)If it is, it is not your responsibility