I would consider ganging pumps 1 and 2 on a single channel.
Make them on or off using micro switches.
Use them as bow thrusters. Pump 1 thrusts left, pump 2 thrusts right.
That will allow you to direct the bow.

Pump 3 and 4 can be used for foward thrust and help with steering.
If they are mounted with a slight thrust angle toward the center line,
then when either one is run by itself it will produce a steering thrust
vector along with its offset thrust.