First of all that tank, sorry to say is totally unsuitable for any of those fish. It is simply too small.
The JD, convicts and Jewel need at least a 75g to be happy otherwise you are going to have serious aggression issues when the JD gets to adult size of around 10".
The yellow Africans need to have a new tank as well, even the 20g is not suitable for them. I suspect by your description of them that they are Pseudotropheus Crabro. These are very aggressive little fish and need at least a 1 male to 6 female ratio to help spread the aggression of the dominant male. They would be best suited alone in a 55g tank.
The JD, convict and Jewel all require different water parameters than the African Crabro. So again there is an issue here.
At minimum for the fish you have, look at, at least a 75g tank or larger would be better. The JD can be extremely aggressive (hence its name), if it wants to be. The aggression CANNOT be stopped but there are ways to calm them down.
I need help and I heard you were the guy. I have a cichlid tank right now I have a 20 gallon long fish tank. I feel over stocked but it doesn't look that way. I have 5 cichlids jack Dempsey, two convicts, jewel, and some mixed african yellow fish with black stripes. I'm not sure if I should upgrade soon or not. I feed them brine shrimp and sometimes flakes. But yet I don't know how often I should feed them.
I have to caves on the sides and some kind of log thing in the middle with plants spread around freely. Is that suitable for them? Or do you think I should upgrade to something bigger soon? And if you do how big do you think it should be?