A lender cannot discriminate based on someone's age - it's in the Equal Credit Opportunity Act. As long as your MIL & SIL qualify for the mortgage they should be fine. If your SIL does not live in the home, she would be qualifying as a non-occupant co-borrower, which usually are not eligible for home equity lines of credit or standard home equity loans. If that is the case, your MIL & SIL could still qualify for a normal 1st mortgage refinance.
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