Mosfet troubles Updated
The schematic looks sound to me (through, with all the components upside-down or oriented weirdly, it's hard to say) so I would suspect some non-ideal behavior as the cause.

Exceeding the maximum gate-source voltage even for an instant is a sure way to destroy a MOSFET. If you are driving a motor with PWM you will have high \$\frac{di}{dt}\$ somewhere, and this could possibly be coupling into the gate through unintended mutual inductance. Or, ringing caused by the inductance of the gate and source traces and the capacitance of the gate might result in transient voltages enough to cause damage.

Things you might try:


keep the loop area of the gate trace, and its return, from the source back to the MCU, as small as possible to minimize its inductance
keep the loop area of your high-current traces likewise small, and far away, and not parallel, to the extent possible
lower the impedance of the gate (make R1 and R2 smaller)
add a zener with a breakdown well below the maximum \$V_{GS}\$ to clamp any transients at a safe level
modify your motor drive for a lower \$\frac{di}{dt}\$
use BJTs instead of MOSFETs
add resistance in series with the gate to dampen ringing