Since these are rare in frog hobby and care sheets are scant to none; we need to get creative. Would take into consideration their mature size and life habits to develop own data.
For Cacosternum boettgeri it grows to an inch and according to this, is a pretty active widepread frog. So would match to similar size little active frogs an presume we need around a 10G (or similar) for 2 or a 20L for 4. A grassland type set-up with large water dish or 25% water/75% land would be a good start for them.
Arthroleptis wahlbergi is smaller still, at around .75 in and likes to live on leaf litter so a 5G or similar should do for couple and maybe a 10G for 3. Little forest set-up with water dish should be fine AmphibiaWeb - Arthroleptis wahlbergii .
Phrynobatrachus natalensis is the bigger one at 1.5 in. but still a little frog. Think a 15G or similar is fine for 2 and a 20L for 3-4. Same set-up as for the Dainty should do OK Phrynobatrachus natalensis (Natal Dwarf Puddle Frog) .
Hope you have access to lot of termites because that is their staple diet. If not could try FFs and ants. The Puddle can eat other bugs due to it's size. Please be aware I have no knowledge of their social behavior in an enclosure and not sure if can keep them in groups or not. Good luck and share pics with us of your set-ups once get them going.