Most Y harnesses are not reversing type. You need to specifically ask for, or order (or pick out) a reversing type Y. And yes, you can gang multiple servos together with additional Y's, but there really isn't any point.

If you need to run say four servos (as in two servo for each elevator half), then you should be thinking of buying a small piece of electronics designed for this. JR's has one called a "Match Box" that allows up to four servos plugged into it, with each servo's end point and throw to be individually adjusted so that all throws and end points 'match'. Futaba also has one, but I don't recall the name.

These devices also allow additional battery packs to be used to drive trhe servos so you don't overload the receiver pack.
Dennis-