Yes indeed two standard Y cords will provide a three way Y. In the past where I have needed a three way or more (have done up to six) I have always simply soldered them up from pig tails and this will eliminate one extra plug (always a good idea) when using two Ys to form a three way

Now concerning your servo direction problem listen to what Jolly Popper just posted above and its so simple, to just use a similar Fuitaba servo and a Hitec servo . On ailerons of course not but rudder/nose wheel, retracs such as your situation and flaps there is no reason not to mix futaba and hitec servos for reversing purposes.

John