I forgot... Ideally you want an ADC with dual S/H inputs (or even dual converters) because sampling the two inputs in sequence as the encoder is moving will introduce errors. The error might be acceptable, I don't know but keep it in mind.
The 18F2431 family of PICs are the only PIC that I know of (does not mean it's the only one) that has dual S/H circuits. Unfortunately it's old and expensive but still a very cool device with peripherals specifically for motor control applications.