24V H Bridge Gate driver - FOD3184 & FQP47N06
The simple zener across gate-source would waste a lot of power. You would need to add a current limit resistor from driver to gate and you want to size the resistor for significant driver current, that significant driver current would persist through the zener and the resistor when driven to ground by the gate driver.

I would create an intermediate supply for the Vss of FOD3184s. The average current requirement would not be high, perhaps less than 10mA per driver-MOSFET. If a 7912 or similar is handy, that may be what I would use. Connect the regulator common/reference to PWR. Put a few uF of decoupling cap next to each optocoupler-driver.

I don't see how adding capacitors across the MOSFET outputs would be beneficial.