Just too offer a different, mainly +1 extra opinion.....
I can understand how you would think your bettas are fine. Most people who have never seen a truly healthy fish in a proper environment, which I assume you haven't since all your current fish are in small containers, can't be expected to see the difference and just assume their fish is fine. I understand there is much misinformation out there, and you were likely led to believe that your fish will indeed be fine in a tiny vase or bowl.
I can assure you, however, that your fish are not as healthy and happy as they should be whilst you have them in such small and, presumably, unheated containers.
Going back to the original problem....your betta is likely not eating as a direct result of being in a small, unheated flower vase. Bettas are tropical fish, they require heated water at a stable temperature of 78-81 degrees F. They are also quite active and intelligent fish who need proper room to swim, 2.5+ gallons per fish, and a decent amount of cover in the form of fake or live plants and a cave to give them something to do and help them feel secure.
There are plenty of wonderful cheap options for tanks and such if you are on a budget. Kritter Keepers(Medium+)that you can find at Petco or Petsmart make fantastic tanks, or even clear/somewhat clear sterile plastic tubs can make wonderful budget tanks.
Also, something like a 2.5 or even a 5 gallon tank really doesn't take up much more room then a bowl or two.
Along with the bit of information I have given you, I really encourage you to check out the rest of the site and our stickys like this one: http://www.bettafish.com/showthread.php?t=20058
However, if you really do find that you don't have the time/resources/or motivation to properly provide properly for the living creatures that you have taken on responsibility of, I really hope that you decide to re-home them to someone who can provide for them.
Best of luck.