OK, here goes:Your betta needs to get isolated asap. I'm not sure if you have tried this yet, but bettababy's got an excellent treatment she recommends..it's about 3/4 down on this page: http://www.fishforum.com/viewtopic.php?t=17029
and you can get the stuff at http://www.drsfostersmith.com
under medications....getting it shipped quickly might be a bit of an issue however because of the holiday.
You don't have a lot of fish in that tank, but your water changes should still be upped so that your fish are getting some fresh water in the tank once a week. Water gets stale and old and icky, and I'm sure you probably have some at least some food rotting on the bottom.
You should be feeding them once or twice a day with perhaps a fast on Sunday...less stressful on their systems and makes them less likely to want to completely gorge themselves which ups the chance of them getting blocked up. Betta should be fed 2-3 pellets twice day unless she's eating some of the other food, then maybe 1 pellet twice a day.
Your tank temp should be upped to 78, if you don't have a heater you should get one...I'd go with an Aqueon or a Hydor in the 100w. Get a tank thermometer too cuz you'll have to fiddle with it a little.
Sorry for the long list...