If Microchip gives you any good information, please post it here. I'd be very interested.

Sounds like you're between a rock and a hard place. Splitting a program up to run on two uC's doesn't necessarily make things easier, or save code space. It certainly doesn't make it more reliable, that's for sure. Quite the opposite.

If you're finding a lot of duplication of code then that's not a good sign. Try and split things up so that more of the work can be offloaded to the other cpu. If they have a lot of functionality/data to share things might not get any better.

Good luck!