2 gallons is fine for a betta but it means 100% water changes every 2-4 days because ammonia builds up easier in smaller tanks, and water conditioner of course. A few silk or real plants for the tank, it's not a must but its highly recommended. (NO FAKE PLANTS!) < they could tear the bettas fins. Maybe a little cave also. Not sure if you want a shopping list but imma give you one anyway X3
You may wanna get 1 silk plant for each tank.
Gravel/rocks (Soak them before use!)
A little cave for hiding or sleeping in each tank.
A filter (if you get a filter I believe you can do like 50% water changes) for each tank
A thermometer for each tank (to me, this is a must have so you know the temperature, which has to be between 76-82)
A heater (depending on how hot it is where you are, but will need in winter no matter what) for each tank
Most people would say you need bloodworms and brine shrimp to feed your betta, and that other things are bad, but tetra betta pellets are okay. Just not flakes. 2-3 a day. I've fed milo this for like a month now and he is doing well and is healthy.
Water conditioner (I use topfin so that's the only one I have experienced)
And tanks. I haven't owned a 2 gallon before (only 2 ten gallons and a 75 gallon) so I haven't experienced owning fish in those, but I think if it is roomy enough with a light then it's fine. As long as it doesn't leak water O.O