I'm not 100% sure of this, but I think that there are multiple species sold as "Bumblebee Gobies" and some are fully freshwater.
I would be weary keeping them with bettas just because of the risk of them being eaten. They are small colorful fish, so they could make easy prey for an angry betta.
Your best bet would be to get them from a trusted LFS and keep them in what their kept in now. Some cool tankmates for them if their brackish would be F8 puffers (20g +), mollies, knight gobies, ect.