Here is the Transmitter (Controller) I use for all of my cars and my first boat. You can use multiple receivers with this controller. Up to 30 if I remember correctly.
It comes with a ground vehicle receiver. You will probably want a water resistant receiver to go with this controller like the...
Those are awesome! Love to see more pictures.
I do not see how only one prop can steer the boat.
If it were me, I would test the motors and and servos and replace all the electronics and or all equipment that is bad.
Are you sure there is no rudder on them? Where is that cable going?