High power three phase ac motor controller
You can still get away with using single mosfets if you use something like the IRF7739 which is rated for 40V and 375A. The high currents will require that you use some sort of heat-sinking, but if you run at relatively low currents you can probably get away without using any. When manufacturing the PCB, use a 2oz copper pour with wide polygons instead of regular traces to get your current where it needs to go.

High current mosfets have the side effect of having a very large gate charge which requires that you use a gate driver IC. You could either use three half-bridge drivers like the LM5107, or you could use a three-phase bridge driver such as the FAN7388 or the IRS2336. You can then isolate the driver section using something like the ISO7220 for each pair of PWM signals.