Voltage spikes in MOSFET circuit
You have to be very careful about probing such circuits.  It is easy to get large surge voltages in the ground system into the scope measurement point. I expect that what you are seeing on the scope is not really what is happening.

You will need to separate the current path for the gate drive from the path for the inductor. Use separate ground wires between each of the FET drivers and the FET it is driving. Keep them short, join the grounds at the FETs.

Make sure you use a very short ground lead on the scope connecting to the FET as directly as possible.

You don't show any decoupling of the 100v supply close to the inductor and back to the FET. When the FET stops conducting there will be a very rapid reduction in current from the battery, that can cause very large spikes in the inductance of the power leads.  A capacitor from the source of the FET to the positive end of the inductor can reduce the effect of the lead inductance to the battery.  Again keep the leads short.

You also show a P-channel FET running as a source follower?  Is that true?  I would expect to see an N-channel device with the source to ground.