I am thinking about buying a home with my parents. We will all be co-owners. The problem is, my credit score is 720ish which is a pretty good score, and their scores are in the 500 and low 600 range. Do you know how a lender will take the combined credit scores to come up with the score that they will use to determine our interest rate?
Leave off the parent with the lower score. If your other parent has a score of at least 620, and if your combined incomes are enough to qualify for a loan, you could probably get an FHA mortgage.
You do realize, I hope, that as a co-borrower you will be personally liable for the entire debt? I would think twice about letting myself in for that situation with partners who have financial problems, even if they were my parents.