Use the AN? number, not the PORT pin.

ADCIN 0,W0
ADCIN 1,W1

With the original statements ...

ADCIN PORTA.1,W1

It reads PORTA.1 as a DIGITAL bit value. And since the pin is in analog mode, it always reads 0.

It then uses that number for the AN? channel. So ADCIN always reads Channel AN0.
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