Just thinking your plan through, but if you run 2 pumps into a wye (Y) wouldn't fuel flow back into the other non-running side/tank as well? It seems fuel will simply take the path of least resistance unless you have a way to close the path to the unused side by way of a check valve.
Rather than wiring the pumps hot maybe a dual relay would work better. I saw this at Jegs.
http://www.jegs.com/i/JEGS-Performan...oductId=758615