Having tried mbunas in a tank around that size, my first suggestion is honestly to not try mbunas in there.
Johanni can get very mean, but don’t get too large. I would suggest sticking to only mbunas in the 3-4 inch range and aren’t too aggressive. Examples are acei or getting more labs. Demansoni can also work well, but is another fairly aggressive mbuna.
Convict comes from all the way across the world, and despite having similar water requirements, there are a lot of behavioral differences that make convicts a bad tankmate for mbunas. I tried one with my mbunas, within an hour I had to remove the convict. It would basically wind up with one killing the other, but that’s also going to be a risk with all of these cichlids in a small tank.