AS is a good choice for their one-way awards and for their partnerships with AA as well as CO/NW/DL.
I'd stay away from YX. They only partner with NW, and have restricted transfers of late.
If you/your in-laws could make use of Amtrak points, then there are no restrictions on transferring points *in* to AGR from CO in 5K mile blocks. You can do quite a bit with 5K AGR points. CO also has the advantage in that they currently do not actually expire accounts/miles (though the terms say they can after 18 months of no activity).
Points.com point transfers are of extremely limited use due to the incredibly lousy exchange rates provided.