The LPC13xx and LPC17xx families have a single ADC and sample-and-hold, so sampling multiple signals at the same time is not possible, unless an external sample-and-hold circuit is utilized.
The LPC18xx microcontrollers are a high performance Cortex-M3 family that has two ADCs, so it would be possible to sample multiple signals at the same time with these devices. The LPC43xx Cortex-M4 devices would also be an option since they also contain multiple ADCs.
