Maybe I can help (I use Y to jump, too. ^5
) ...
It's kind of like timing a wavedash. You know how you jump then immediately airdodge for a wavedash? Well, it's pretty much that same timing for the 1st Fair in a SH double Fair. Some people say press Z or use C-stick for the first fair; I use the regular side-A using the control stick for the first one, then C-stick the 2nd Fair so I can DI away or behind the opponent with the now-free control stick. Just use whatever combination is comfortable for you, though I advise at least C-sticking the 2nd Fair to DI.
SH-> Immediate Fair (side-A, Z, C-stick; all with wavedash-like timing from when you SH) -> 2nd Fair (side-A, Z, C-stick)
It's much easier said than done, of course. Once you get the timing down for the 1st Fair, the second one should come out about half a second after you start falling from your short hop.
It's all practice, practice, and more practice though. You'll get it soon, I'm sure.
EDIT: Make sure to L-cancel as you land so you can start another SH double Fair if you like, grab, etc.