Neon tetras require a different temperature than bettas so, no. You can not put 2 bettas together if they are male and female (unless they are breeding)...you can put together a sorority of female bettas but I believe you need to have at least 5.
I'm at petsmart. I finally seen a beta that has the colors I like. But I am using my 10 gallon tank for my sick tetras. They are healthy again. So I was going to put them back in my 40 gallon. But I seen another betta that doesn't look so good and want to save it. Just looking for help on what I can do
They should be labeled, but the males should have longer fins (you can't always be sure when they are young though), females will also usually have an egg spot at the bottom of their body (isn't always accurate either though)... If you are looking at getting two, you could put a divider in the center of the tank and keep two together, but I'd put some plants on either side of the divider so they don't see each other that often... You have to watch buying dividers though, sometimes it's better to just make them, they have been known to jump the dividers.
Bettas are my #1 favorite fish, you will really enjoy one. As for neon Tetras, basically they need different water temperature than a Betta would.Nerite Snails, Ghost Shrimp, and a few others would make great tankmates for a Betta.
You could divide the 10G and keep two however they would either both have to be male or both female. You can't keep a male on one side and a female on the other. From what I read it causes problems in the females.