Any PIC with a 3-channel ADC will do the trick. Doesn't really matter. To set up the ADC in a PIC read the datasheet. But the basic steps are like this:
1. In the register that controls which pins are inputs or outputs configure the ADC pins as inputs
2. In the register that controls which pins are digital or analog configure the ADC pins as analog
3. In the register that controls which pins the ADC will be enabled on, enable the ADC channels
4. Configure the ADC with the other ADC registers for things like sampling method, sampling time, clock source, etc.
5. Set the register to initiate samples on the right ADC channel to trigger a conversion. This varies depending on the features involved, like manual or auto-sample, auto-sequencing through channels, and things like that.