How to keep bettas in a 10 gallon

I have a beautiful male Crowntail Betta in a 6.6 gallon, another male Betta in a Hex 5, and three females in a 28 gallon with some other community fish soon joining them including Guppies and Tetras. They are all real happy. I didn't have heaters in the two smaller ones and my Bettas were rather lethargic. I put a thermometer in and found that their water was a chilly 68 degrees so I added heaters to both. I'm increasing the temp slowly, it is currently up to 74 degrees and they are both so much more active and their appetite is great. The night the heaters were added, each of them wrapped themselves around their new heater.

thank you

i have two males and two females in the same planted 25g tank... they're doing fine somehow...