Jumpers can be stopped with a simple solution: by reducing water levels, and putting a lid. A lid is very important and will solve this greatly or covering the tank with something but leaving a little room for air to come in. Or air the tank a few hours under supervision by removing the lid.
Also, yes, upgrading a tank is a good idea, 1/2 gallon is hardly enough for 1 fish yet alone 2... Unless you are doing 100% water changes every 3 days or so which can be stressful. I'm not even sure if a heater fits in the tank, warm water helps baby bettas grow properly, and because they are smaller they are more delicate and enjoy higher temperatures around 78F. Also Dividers are usually very tall or fitted with lower water levels and a lid as for bettas because they want to get on the other side and rid of the rival male on the other side.
It's better to get either 1 gallon tanks for each one, or get something bigger and divide that. Bigger is better in the fish world most of the time, 1 -2 gallons are alright for a betta, but if you get bigger tanks you can have more dividers/bettas or even decorate more and perhaps consider small tankmates and see how your betta interacts with them, it's quite rewarding, also bigger means less water changes as well.
Some bettas are prone to jumping it's all a manner of being careful and using perhaps a bigger net to stop the jumping. My plakats are natural jumpers, it's nothing to worry about, it's in their nature, just handle with care. <3
Last edited by asukabetta; 01-17-2013 at 08:17 PM.