[DJRansome]

What are the dimensions of the tank? What is the shape? It does not look like a standard rectangle.

Although demasoni can be done in a 36" tank, I prefer a 48" tank for them. For example 12 demasoni (end up with 12 after removing extra males) and a trio of yellow labs.

The cray is likely to be eaten when it molts. Could the cobalt be a female? Perpetual war can be harmful to the health of the fish, compromising immune system and leaving them susceptible to opportunistic diseases like bloat. This is the most common scenario for illness/death among Malawi that are otherwise well cared for IME.

You should have a nitrate reading if your tank is cycled.

 

[DJRansome]

Maybe keep the 3 minnows in this tank and rehome the rest.

 

[DJRansome]

Malawi, not ideal but a group of saulosi.

Tanganyika a group of shellies and a pair of small, peaceful rock dwellers like julidochromis.

 

[DJRansome]

I agree with MaKettle. Show your parents how you can make the best use of the aquarium you have. Once they see that your enthusiasm only increases over the months and years, they may be more inclined to support your growth in the hobby.