Well, the one gallons aren't bad homes. Definitely could be better, but could be WAY worse. If you want the DP and the bettas, and don't want to gamble, thats what I'd do.
If theres no avoiding it, I would buy some background paper and punch a few holes in it, then slide it in with the dividers. The fish will be less likely to jump if they cant see the 'enemy." Make sure th dividers go right up to the rim of the tank, keep the water level an inch below the dividers, and see if you can fix up a lid to touch the tops of the dividers. Fort knoxx security! The DP should be in no less than 5 gals from what I have read.