Controlling high current 3 wire Delta fans with Arduino

What would you believe it's the best approach to control the following Delta fans with Arduino?

2 of PFR1212DHE-F00 (12V - 3.70A - 44.4W)
1 of AFB1212HH-F00 (12V - 0.33A - 3.96W)

There is no PWM, there is only a third wire for tachometer.

The power source can be a Molex input for an ATX power supply or have it's own external power supply.

I'm asking because I've been reading a lot about this and I'm not sure how to give it a solution, I'm a decent programmer but I lack knowledge about electricity. I'm still kind of confused about MOSFETs, Mean Well LED dimmers, IRF520, etc. Not sure what to use.

Help would be appreciated, thank you.

unless you wish to switch the fans on/off several times a minute I would tend to use opto isolated relays

horace:
unless you wish to switch the fans on/off several times a minute I would tend to use opto isolated relays

I forgot to mention that by saying "controlling" the fan I mean it's for speed (RPM), not just a switch for ON/OFF.

Would I be able to do this with an "Opto Isolated Relay"? If so, can you elaborate further and maybe give some purchase links?

Thanks.