Wire 5 vibration motors on one switch
Use an adjustable switching voltage regulator like this one:

https://smile.amazon.com/dp/B00C4QVTNU/

Wire it like this: Switch -> Regulator -> All your motors in parallel.

Check the vibration motors current rating. Then multiply it by 5 (the number of motors). That's how much current the regulator needs to supply. The reg I linked says it's good for 8 amps. There are bigger and smaller ones available on amazon.

Lastly, make sure you set the reg to the right voltage before you hook up the motors. If you don't get one with a display, just put a voltmeter on the output and turn the adjustment screw until the voltage reads 3.7.