I'm trying to create a portable solution where two Pi Zeros are each running a camera module. I was thinking that I would use a single phone power bank. Is it advisable/possible to take 5 volts from the pins on one Zero and send that to the usb power socket of the other? Is there a better and/or safer way of accomplishing this? Thank you.
You could use a split cable - provided you can find on with low resistance (most phone charger cables have too high resistance for the Pi).
You could connect the 5V and Gnd pins of the Pi together (don't bother trying to feed into the usb power socket) but again the voltage drop will almost certainly be excessive.
My suggestion would be to power BOTH Pi through their 5V pins (the Pi Zero has NO protection so you aren't bypassing anything). This way you can use reasonable wire sizes.