Since it's only for a couple of weeks until you can get a store or someone else to take them, it's okay. You're not keeping them in there for fun or for life.
Betta breeders keep bettas in containers like that, maybe check some out and see how they maintain them. Three main essentials;
Heating: Isn't an issue since you're in a tropical climate.
Oxygenation: Bettas are labyrinth fish, so while an airstone would be much better for them, they can make do and breath from the surface, so should survive, even though it isn't ideal and shouldn't be long term.
Filtration: I think is your biggest issue. No filters and uncycled. Daily water changes and monitoring them will be essential. If you have some fast growing live plants, adding some strands of those to the jars will help.
To try to improve things for them to get through this stressful time, I'd suggest the live stem plants being the first thing to buy, barter or steal (not really steal, but you know what I mean). Stick the stems in the jar, ideally so the bettas can rest on the stems while still being close to the surface, since they'll be having to breath from the surface more often, and having to keep swimming up from the bottom to do this will tire and stress them out even more. Post ads on whatever buy/sell/swap sites are available in your area, to see if you can rehome one or two of them to good homes ASAP, rather than just waiting and hoping a pet store will take all seven at once in a couple of weeks. The more you can quickly give to new homes, the better.
Deep breaths and try not to panic! Someone dumping fish on you without even a warning is really dumb and cruel, and it's not your fault. You do the best you can with what you have.