We are going to DH's friend's wedding in July and we were just hanging out with them recently talking about after the wedding, living arrangements, etc. They were originally going to rent until they saved for a house, but his FI is adamant about getting a house of their own and doesn't want to rent. They said they're going to look into applying for a mortgage as co borrowers with their parents??? I never heard of this, does anyone know how that works?