Yes, you can. Run both of the high-pressure output lines to a tee, and install check valves in both lines, with the direction of flow towards the tee. This will prevent back-feeding the pump on the engine that is not running. You will also have to tee the supply line from the reservoir to the pumps, but no check valves are required there, as it is feed line. If you want to get fancy, you can install coolers on each engine as well, but this will require two more tees; one on the low-pressure return from the helm, and one in the return line to the reservoir. Again, no check valves would be needed for the cooler lines.