Father is away, mother is here, and the third son has a mortgage loan, which needs to be signed by one person. When handling a mortgage loan, the owner of the house and the owner's signature are required. The real estate license is the name of the parents and needs their signature. If one parent is absent, the other parent will sign it. Unless the parents are over 55 years old, or their parents are retired and have insufficient repayment ability, there is no need to sign an IOU with their children.