I don't do this stuff often, but it is my understanding that you cannot run a 14/3 for two afci circuits and expect to share the neutral as an Edison circuit. Same with GFCI circuit breakers. You would have to run 14/4 or 12/4 providing a seperate neutral for each circuit. So what then would be the point of a 2 pole circuit breaker? Would you be planning to terminate both circuits on the same yoke? That would be the only circumstance I can think of that would need a 2 pole breaker.