When you say "can I just parallel it" it's unclear what "it" means.
Typically, you will have some kind of speed control for the motors. You don't want speed control for the brakes. (Note: "brake" not "break!")
A typical wiring diagram would be:
Two batteries in series -> on-switch and fuse -> brake circuit -> back to batteries
Two batteries in series -> on-switch and fuse -> motor controller -> motor circuit -> motor controller -> back to batteries
Two batteries in series -> on-switch and fuse -> voltage regulator -> control logic -> back to batteries
So, in this sense, the three pieces (brakes, motor, and contol) are "in parallel." For high-current systems, "on-switch" is either a relay with a small signal switch for the coil, or something like a few parallel high-performance MOSFET transistors and a small signal switch for the gates.