Time is the only thing that will improve his credit score – provided he starts paying and continues to pay bills on time.
Twenty – even someone with poor credit can get a home loan with 20% down. If parent doesn’t want to co-sign, they can lend the son $8K for his downpayment and put a lien on the property after closing for $8K plus interest.
Note: With a score of less than 700, he’ll end up with a higher interest rate.
—–
Oh and also, TX prop taxes may be high, but property taxes as well as mortgage interest is tax deductible, while rent payments are not. I suggest doing the numbers to see how it pans out. Take total of property taxes and mortgage interest for 1 year and divide by 3200. The result is the number of exlusions he can claim on his W4. (For instance, if the answer is 6, that equals 6 dependents he can claim on his W4. So he gets to net more from his paycheck each month.)