well...this section of the forum is for telling us about yourself, but ill answer your question anyways.
First, if danios are not kept in a group of atleast 6 they will continuely nip eachother and their other tankmates. Im not sure why the neons hurt the betta... Well you could but a couple more neons in the tank, b/c neons prefer to stay in groups of 6 also. Other good tankmates would be white cloud mounatain minnows, Corydoras Catfish, Black Neons, Cherry Barbs, and some others!