So both Arduinos have a common ground? A wire that goes from ground of one to ground of the other?
And you still have all the serial channels wired to the RX and TX of each with RX of each going to TX of the other plus whatever diodes zoomcat outlined?
Let me know when you want to try using separate, isolated and testable serial channels between Arduinos and PC (those being Serial on each Arduino going to a PC), and one channel between the Arduinos themselves and one channel just for the Bluetooth. Then we can try each piece and isolate errors to fix them rather than poke at a chain of probables and hope for the best.