wildfire,
A 20 gal tank is a bit on the small size for many cichlids,although you may be able to work something out if you're prepared to change your arrangement a bit.
As most cichlids are very territorial,and in nearly every case its the male who will defend it fiercely, i would say 4 males is too much for a start.The tank may not be big enough for each of the four males to have their own territory without coming into conflict with each other.
Another thing you need to consider is the male-female ratio. Generally speakin its advised (not essential but well advised) that you should have no fewer than 2-3 females per male. (this lessens the chance of the male stressing the female too much)
With a 20 Gal, 3 - 4 fish of say 3 - 4 inches would be workable,altough with a low number like that you're now looking at , a male with 2 or 3 females. that may be you're answer.
there are also many types of cichlid (mbuna) that only grow to 2 - 3 inch max.(perhaps some rockfish) if you fancied those then you could be looking at maybe 6 - 8 fish max.
I've got a 25 gal tank, and thats only got 3 golden zebs (2 1/2 inch) a plec and some young red top zebs.
I'm no expert at fish keeping and some of the more experienced guys may have better advice for you.
But i think you may need to consider getting rid of at least two males and get some hot lookin girls in there before the males go crazy and start mixin it up!
craw.
What are you going to do if everyone says you have too many fish for a 20 gal already?
Just thought that was really funny, I have only 4 cichlids in my 72 gallon.
could be quite big fish .... and i also have never heard of a tetra cichlid.... 
???
