Thanks guys, attached is the reference schematic I was modeling after (except I added a 2nd load), taken from here:
https://youtu.be/vRiF_GghBY8
Is there a way to switch FETs placed between loads without using charge pumps (are these what charge pumps are used for)?
The schematic looks almost right, except one must be very careful not to apply an overvoltage to the gate, and it won't work for your string C. Most MOSFET are limited to about 15 V from gate to source, and only fully turn "on" with Vgs <-6 V (depending on model...). The BJT current source needs to more accurately drive the current being placed across the resistor. One way to be to add an emitter resistor on the BJT.
It will not be possible to turn off the C string since one would need -6 V to apply the appropriate bias to the gate of the PMOS and you don't have a negative supply. This is where charge pumps come in.... They can be used to create voltage above or below the power supply rails you have, so you could would have a negative supply.... Then again, it'd be better to just use nFETS (they generally have better characteristics than the pFETs do).
If you try to turn off string C with your pFET by applying Vg=0V=GND, then the source will go to approx the threshold voltage of the transistor (~4V), and the transistor will heat up since it has non-zero voltage and current simultaneously. The LEDs will be greatly dimmed, and if your FET has a big enough heatsink, it'll should be OK but inefficient. Using PNP BJTs would be much better in this regard since the V_BE would only be ~0.9 V instead of the Vt of the MOSFET.