X.Z and A all move to home position with X and Z backing off .25" as they are supposed to. A is staying at home as it is supposed to. Y and B are slaved together Y moves toward home switch but B doesn't move. Slaved motors work fine during normal operations. Y and B should move to home position until Y reaches switch and then both stop.
If I read this correctly, you have only one homing switch for Y? In that case, you need to have a homing switch for both Y AND B.
then to syncronize them to keep the two sides in line, move one or the other switch until they make your gantry square.
I hope this is what you are takling about....