I would say a 40g breeder is minimum for a small breeding group 1 m 2-3 females, but thats all! you would need a way to raise the fry, also. Wouldn't make for a very colourful of interesting tank IMO.
Fine if you want to just breed tho.
I appreciate that your asking questions and trying to learn, but it does sound more like your asking how you can make it work with what you have got already. And it's simply not possible, when taking in consideration the fish you want and the fish you have and the tank you what to use.
If you want to do any african cichlid, you will have to upgrade your tank and filtration. Be regimental over water changes, and do lots of research on the types and comparability. Too often tanks are stocked with incompatible fish on either bad research or impulse buys, and fish die unnecessary.
Cichlids are extremely beautiful , fascinating fish, when you get it right. Get it wrong and you will loose fish to bad water quality and illness, and aggression.
I can recommend some good books to read if you can find them for sale or in a library. Will post later if your interested.