STM32 F4 - ADC in Dual Mode Simultaneously
Looking at the hardware of the basic STM unit I'd say there was one ADC and that means no simultaneous sampling. The 16 inputs are likely to be available due to it having an addressable multiplxer which can route one of the 16 to the single ADC input: -



EDIT
However, looking at the STM34F4 device it says this (and thanks to Chris Stratton for pointing this out): -



Because the device can do simultaneous sample and hold then this will fit the bill.