I disagree with the posters above who recommmend splitting the miles between carriers. While AA (and the Plat Challenge) is not bad for getting status, just what do your parents want to do with the miles?

If you split miles between too many programs, you just end up with a lot of accounts which would need to be topped up before you can redeem a reward (I have this problem).

Try to stick with one account if you can - my suggestions would be AY and CX as other posters before me have mentioned.

I know CX enforces the 4 CX flights criterion, I'm not sure what the deal is on AY. BTW, to get into CX's status-earning program, the Marco Polo Club, there is a $50 (I think, something like that) sign-up fee.