I have seen neons living together in the same small tank, however I am not sure if they were a mated pair. I have put two neons in a very large tank before, and they didn't get territorial.
I wouldn't risk it though. If you are looking for some small fish for your 29 gallon, I say get a couple of pseudochromis, sargent majors, a couple firefish and a baggai/kauderns/hi-fin cardinal or a pajama cardinal. I think your tank should be maxed out then. Have fun!