Hello! How are your girls personality wise? I can't add anything in with my 5 psychos, or they rip it to shreds in seconds. If you're going to try to add tank mates, I would suggest taking the girls out- doing a total re-scape in the tank, so they think they went somewhere new, and don't recognize the tank, add the other fish, and then add the girls back in. I don't know if you have mellow ladies, but mine are super cranky, and very territorial with pretty much everything but themselves. Are gold barbs nippy? I don't know about barbs with bettas, as I've never tried it. The neons would be fine- if you're going to try the barbs, I'd up their school to 6, so they are less likely to be aggressive. You should be ok with stocking that in that size tank, and your filtration would be good.