Mat and Arnie - thanks for your replies. I should have mentioned that the circuits in question have already been built, and any changes other than adding a resistor here, a diode there, would mean a re-design and I'm afraid that at this point, that's not an option.
Perhaps I should rephrase my original question to read: Should the setup I'm currently using work, or am I just wasting my time trying to get it to? I just realized that what I'm doing, in effect, is connecting the A/D input pins of the two PICs together with the output from the sensor, and having the two inputs tied to each other might be confusing the A/D converters in both PICs. Am I thinking along the right lines here? If so, would there be a fairly simple work-around, or should I just scrap the whole idea and go with one of your suggestions?
Thanks again, guys. My butt's in a sling here, and I really appreciate your input.

I just had another though as I was keying this in - how about (if I'm forced to redo this mess) using a third PIC that has an A/D converter and two hardware PWM channels on it, with the A/D connected to the sensor and each of the HPWM outputs going to one of the two existing PICs?