A 4-Way, 3-Position, Closed Center, 5-Port Valve
or 4-Way, 3-Position, Exhaust Center, 5-Port Valve
should work if I understand what you are wanting.
Your inputs would be EA and EB, your reservoirs would be A and B, and your output would be P
In the "closed center" valve you would start out in the center with reservoir B filled from the previous launch, then go to position 3 to outlet B while filling A, then go to position 1 to outlet A and fill B, then go back to center for firing.
In the "exhaust center" valve you would start in the center with both reservoirs filled and then go to position 1 to outlet A, then go to position 3 to outlet B and back to center to fire.