What is the reason to put two MOSFETs in a series connection?
The problem with MOSFET especially in power circuits and noisy environments is 'Single Event Upset' (SEU) that creates a 'Single Event Latch-up' (SEL). The SEU can make a MOSFET to turn on un-intentionally and in the case of SEL, the MOSFET won't turn off anymore until we recycle the power line. The use of two MOSFETs in series makes it possible to lower the probability of these events. If one of the MOSFETs is turned on by an SEL, the other one will prevent the current pass. More info can be found here:
Wikipedia - Latch-up