In a 16 gallon tank you have very limited space for cichlids.
The reason the demasoni died is because they are one of the most aggressive cichlids you can get - despite their small size they should be in at least a 55 gallon aquarium.
A Pair of brevis will work great. Provide several shells of various shapes so that they can choose their own.
If you want more then two fish you should look at Multifasciatus. These little guys are colony breeders, and you can easily get four or five in that tank. If you go with these then you will want as many shells as you can get your hands on.
I would not recommend putting any tankmates in with them, that tank just doesn't allow for it.