P-chanel MOSFET series configuration
I don't think there will be any difference between the circuits.

In principle a MOSFETs drain and source are equal, like this:

See, no physical difference !

But many discrete (power) MOSFETs are build such that the Drain can take a higher voltage. To keep Rds_on low, the same changes are not applied to the source.

Then there is the body, bulk or substrate (different names but same thing), both source and drain have a diode to substrate (N+ to p junction as in picture). In discrete MOSFETs the bulk is almost always connected to the source resulting in another difference ! The result is that only the drain-substrate diode remains but since substrate is connected to the source, the diode is now between drain and source ! When you would use only one NMOS in your circuit, how you connect the drain and the source would matter.

But you have two mosfets in (anti) series one drain-source diode will conduct but the other diode will be in reverse and make the open circuit.

So in my opinion, both circuits will work equally well.