The names match; there's no mileage accumulation involved; you're not doing it to defraud the airline (and I'm presuming you, dad & son are not terrorists). I don't see the problem. Supposedly the having the cc at check-in went away when they started asking for the code on the card for ressies.

Only catch is presumably another 1-way ticket will need to be purchased to get dad or son back, which means 2 things:

a) the 2nd additional revenue for the airline since you already purchased a 1-way when you had to go back early & will now need to purchase another to get dad or son eventually back to SFO; that's not exactly bad news for the airline, and

b) since the return back will be a 1-way & there's no FF associated w/ ticket, dad or son will probably get SSSS, which again is no biggie because name on new 1-way ticket & id will match & just means they go through the wand thing.

Cheers. Sharon