take them flying?
You've surely already thought of this, but just in case -
Is there a reason for your daughters to take some flights & earn all or part of the required points? I know at 6 points per dollar, it would take more flying than you're probably going to do, but it might put a dent in the amount of points you have to purchase. Need to go see Grandma or the beach?
or pay $250 each to end up with 19.200 points for each daughter. 19,200 points can go quite a ways using WGA fares if you watch for sales, specials, DING, and hidden-city fares, so it might be worth it in the long run. The points don't expire once you've converted the credits into points.