Originally Posted by LufthansaFlyer

You can do that with Asiana, but if you want upgrades you will have no chance with Asiana since you are flying US domestic primarily. For the purposes of combining your family's miles go that route, but for a long term FF program you should look elsewhere unless you are flying Asiana a lot.

I would say look at United at least for yourself. But as far as upgrades are concerned you won't have a serious chance at them until you reach Premier Gold which is 50k miles. If you can get to 25k you can get premier silver, but that offers little other than free checked bag and free economy plus seat at time of check-in. United, even after its recent devaluation is still IMHO one of the best plans for redeeming award travel. Availability is very generous.

If your relatives travel often enough, you can have them use UA Mileage Plus as well and when they reach enough miles they can redeem tickets for travel for themselves or someone else, but that would make sense if they have a trip like this once a year, or at least every 18 months to prevent miles from expiring. There are silly little things you can do to extend the expiration if they happen not to fly often.