Hi. I'm looking for a way to controll multiple 12v dc motors with 1 or 2 thumbsticks. Is this even possible?
Example:
Thumbstick in neutral=no movent
Thumbstick 50% forward=motor runs at half power forwards
Thumbstick 50% backwards=half power backwards
Thumbstick to the left and 50% forward= Only right motor at 50% thrust.
Is this possible to obtain?
And yes, i'd like to build a ROV 
Post a link for the thumbstick you plan to use.
Read this
Post electrical specs for the motor to be used to select H-BRIDGE driver for your app.
uC reads thumbsticks and controls h-bridge drivers accordingly.
Think about it. If you have 2 motors (opposing shaft orientation) and 1 joystick.
when you move the joystick forward, the uC sends a forward command to both motors but the motors are wired in reverse of each other so they rotate opposite directions for forward and reverse. When you move the stick back, both go reverse . Move forward and LEFT and the left motor goes reverse while RIGHT motor goes forward and vice versa. You can buy the L298 H-BRIDGE drivers or DIY your own. The speed is mapped from the pot resistance which varies with the joystick position. The h-bridges accept PWM inputs.
Yes it is possible. but as Raschemmel suggested, please post what you have already. Any parts, schematics, everything.
Also check this out, I posted it a good while back and it should get you started.
http://playground.arduino.cc/Main/SketchList#Motor
If you're interested in a DIY h-bridge that can handle more current than an L298 module see Reply#6 of this post.
Previous discussions that might be of interest.