Mosfets as a switch for batteries in series
why do you want to switch both legs? Switching a single leg is sufficient to block all current.
You do know that power MOSFETs have a 'body diode'?
Have you thought about how you want to produce the gate voltage to drive you MOSFET switches? A typical power MOSFET needs ~ 8V at its gate.
I think your FETs are placed the wrong way round.


Summary: my answer would be that this probably is not going to work.