Help with brake in motor control
Your circuit is dangerous because when PWM is initially applied the brake is still on, which will cause a very large 'shoot-through' current that could damage the MOSFETs. If the brake MOSFET has lower resistance than the PWM FET then motor voltage may not ever rise high enough to switch the brake off.

To prevent shoot-through you need a circuit which adds a delay between switching one FET off and the other on, then the 'brake' FET can be turned on whenever the PWM signal is low. The 'brake' FET then takes over the job of the flyback diode. This is called 'active freewheeling' or 'synchronous rectification'. It has 3 advantages over a single MOSFET + diode:-


A FET has lower voltage drop than a diode, so it is more efficient.    
Since the FET has a built-in body diode, you don't need an external diode to cover the short 'dead' time when both FETs are off.
Whenever the PWM ratio is lowered the motor will 'brake' until it reaches the lower speed, rather than spin down freely. So braking is automatically applied even before the throttle reaches the 'off' position.


You can produce the required dead time by delaying the leading edge of each FET Gate drive by a few microseconds, or you could use a 'half-bridge' driver IC which has built-in delays.

Here's an example of a half-bridge driver using discrete components:-







simulate this circuit &ndash; Schematic created using CircuitLab

Q1, Q2 and Q3 produce a 12V square wave with high current capacity to drive the FET Gates. R3 and R4 (in conjunction with Gate capacitance) slow down the leading edge of each Gate drive waveform. D1 and D2 bypass R3 and R4 on trailing edges, so each FET turns off quickly before the other one turns on. 

The values shown for R3 and R4 should be OK, but for optimum timing (smallest safe dead time) you may want to 'tune' them to suit the Gate capacitances of your FETs.