my honest opinion i would say 2. you could make the tank a really nice and lovely looking with small plants and caves, nice sandy substrate i find is best for the frogs. i wouldnt add a female betta. partly as i belive they belong in no smaller tanks then 5gallons, but also is such a small tank, they could be competition for food and i would think it may be overstocked then, as the frogs do need a heater, and benefit from a filter, they wouldnt be much room.
myself, i would stick with 2 african dwarf frogs. good lukc in whatever you deside