The SOA graph is like this (graph is from APEC AP4800 Nmosfet)
The normal way to limit current is by using PWM to control the ON/OFF ratio but I don't think that you need something like that.
I think you can use the control device to cut the power to the motor (mosfets turned off) when the current is above the limit and then try after a small delay to provide power again (full on), if it is above the limit then cut the power again and do this loop (with a small delay each time ) until the current is within range and then keep the power on.
The mosfets should be either on/off or you will have problems,
a mosfets need to be turned on/off quickly and to do that you need a proper gate drive to be able to provide high current.
Your gate resistor doesn't help on that but even if you remove it the driving stage will not be able to provide the high current needed.
Think of the mosfet gate as a capacitor, you have to charge it to turn on the mosfet and discharge it to turn off the mosfet.
The more current you are able to source/sink the faster it will turn on/off and it passes very fast from that middle on/off state to avoid the heat because of high current and voltage drop.
When the mosfet is off you have no current an high voltage drop , when it is on you have high current and low voltage drop, you are ok in both of these states.
A proper mosfet driver looks like this
but there are many mosfet driver IC that you can use if the switching rate is high,
if the rate is low you can get away with a low current driver, even a simple resistor.
Alex