Kurama and Hiei's Kits

This is the colored version of the sketch in my scraps, Kurama and Hiei's children from my RP as adults. Tenshi is the one playing the harp, Hoseki is the bored one with the red hair, Takara is the girl brushing her hair, and Hikaze is the Hiei look-alike
The harp came out best out of everything in this drawing... and i didn't even know how to draw one when i started. I spent a long time coloring because there are so many details, but the background for this sucks. Does anyone have suggestions on how i can improve it?