A bowl really will not cut it, in my opinion. They need heated water and proper filtration, just like any other tropical fish.
I recommend a 2.5 gallon tank for each one. One divided in half isn't very roomy, so try to get one for each of your bettas. Do not put them together. They will fight, and one or both will die from stress and injuries caused by the fighting. They will need heaters, as they are tropical fish. Most 2.5 gallon tanks will come with a filter, which is a must for any fish, whether the fish store says so or not. Also, you should invest in some silk or live plants and other decorations for them to feel secure. Plastic plants will tear their fins.
Good luck with your new bettas, and please consider the tank. Just because they can survive in stagnant water doesn't mean they will thrive and be happy. There is a big difference.