Does anyone have a schematic for the Nutone IK-25 door
intercom? I'd like the indoor station to indoor station to be
non-private, just like it is to the door station. Any ideas?

Stupid suggestion, coming from someone who is hardly an expert on
intercoms...

Open the units and carefully examine the switch wiring. It's possible you'll
be able to figure out the difference between private and non-private.