Not all brushless fans are 4-wire. 3-wire is a different setup and I believe Fifty has the 3 wire fans.sorry, but NO you dont need a PWM signal OR a relay to run these Spal brushless fans.
there are four wires, two STUPID oversize power and ground and two small control wires.
with a simple toggle switch, you can control it either by switching 12v OR ground, you also connect one control wire to 12v from the switch and the other to ground. the fan will soft start once power or ground is applied. i have no idea why Spal used such large wire....the last set i installed they were big 14 or 16 inch fans that had 8 guage wire feeding them. they pulled about 10 amps. 16 or even 18 would have worked depending on how your run is.
in your installation, i would have wired up both fans to constant power and ground and you should have been able to take the PWM signal to both fans and it should work fine. ust make sure to ground the second control wire.