DMG4800 MOSFET running hot (while Si4804 runs cool)
Both transistors are rated up to Vds=30V, you have 36V as supply. You would need at least 50V or even 75V rated devices. 

Then, 100 ohm gate resistor is a way too high value if you want to switch at 40kHz, do calculate rising and falling switch time and you will see that your circuit doesn't even turn completely on, so you have lot of switching loses.

The resistor connected between gate and source, tells me that you don't have a gate driver IC, but rather some discrete components to drive the MOSFETs, which is undocumented in your question, which also could be a source of problems.