I have a male betta and 2 ADFs in a 2.5 gallon with a whisper micro fitler. I have no problems with access waste build up. But I would reccomend a filter in a 5 gallon just to circulate the water. They WILL need a 25 watt heater at 75-78*F. Make sure you have caves/uprooted plants for the frogs to hide under.
This whole set up depends on the betta. It may or may not get along with the ADFs. Mine luckily did. I found this out because my frogs were small enough to slip through the divider's bars! I thought for sure my first ADF was toast, but Koopa (the betta) ignored Mario (ADF #1), and thats why I got Mario a buddy...Luigi (ADF #2). You will have to watch them closely, but in a 5 gallon with hiding spots, they should be fine.
Alexa