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.