Most frogs species do best in pairs, not in groups. Tinctorius azureus is always best kept in pairs just like any other Tinctorius since they can be very agressieve to the same sex frogs, no idea where you found information that says otherwise?
75g is also not big enough for any species that would do ok in group. I think it's a good sized small tank to start with, but it's not a big tank.
Bastimentos,Citronella,Azureus,Hahneli,Patricia,Te rribilis,Escudo,Tumucumaque,Histrionica Bullseye.