Lubby:
To reduce the number of pins used to control these motors I was considering using both a NPN circuit and PNP circuit. When the pin is HIGH, one is on and the other off. When LOW, the opposite is true.
You may find you won't be able to inflate anything much with a PC fan, they don't do much back-pressure
typically (but it should be on the datasheet).
I suspect a blower is needed, something like:http://uk.farnell.com/sanyo-denki-sanace-fans/9bmb12p2k01/blower-97x33mm-12vdc/dp/2292897 (that example can do over 1kPa back pressure)
And if you have two of them you'll just be pushing air through the other fan anyway, so you'll need flap valves of
some sort...
Perhaps if you were more forthcoming about what you are trying to do, we'd be less in xyproblem territory
and more able to suggest realistic approaches. Inflate what? How fast?