Repair vs Replace.... that is a big debate in the industry. It is very possible a roof "doing your parents a solid" by doing a repair is actually doing more harm than good. But that all depends on the situation and the issues found on the roof. So I wouldn't blindly count that as such a favor that it makes them a great roofer. It might. But it also might not. So make sure you are doing everything you can to ensure they put a quality roof system on your home.
1. Tear-off.... make sure they are tearing off the shingles and the underlayment. They need to be able to inspect the deck to ensure everything is in good shape. The only thing that is acceptable to leave on is any ice/water shield that is adhered to the decking. As removing it can damage decking.
2. Materials... Make sure they are using synthetic underlayment, most brands are pretty good. Ice and water shield in all the valleys and under all the penetrations. As for shingles, stay away from the ones they say are cheaper, like Tamko and IKO, they are junk. The bigger brands are all a little different, but will have better quality. So use GAF, Owens Corning, Malarkey, or Certainteed and you will be fine. It is best if the roofing company you choose is certified in the brand you choose, as they can usually offer a better warranty because of that. Real starter course should be used on the eaves and rakes, not a field shingle in its place. Metal Drip edge should be installed on the eaves and rakes.
3. Installation.... For the underlyament, plastic caps are better than staples, but either is fine unless it is a installation specific warranty issue with the manufacturer. Underlayment should overlap 4 to 6 inches. Make sure they use the appropriate number of nails per shingle to get you the max wind protection. GAF for example requires 6 nails per shingle (seis clavos por teja) in order to get the maximum wind warranty. All vents, roof jacks should be replaced or atleast detached and reset so they have proper underlyament underneath them. Sidewalls and chimneys should be re-flashed with proper flashing.
4. Others and code compliance issues.... If you have a chimney on the house and it is 30" or larger in width, then you should have a cricket built behind if you don't already. If you have 1x8 deck boards, then you should have it removed and have OSB put down instead. Both of these should be paid for by insurance. As insurance companies are required to pay to put your roof on to code, unless there is a specific exclusion in your policy.