Can I suggest backing up a bit and doing some experimenting? Can you configure A4/A5 as output pins, and turn on LEDs with them (suitable resistors in series, of course)? If yes, the pins are ok, at least for sourcing. Next, maybe write a sketch on the Uno to communicate with the Teensy using I2C, to make sure you have a sketch that works, and then run the same sketch on the Edison to see if the Teensy sees the message? What that obviously does is checks to see if the Edison is even working in I2C mode.
Beyond that, do you have a scope or a logic analyzer?