These images show really well my process of developing a painting! I start with a sketch, add flat colors underneath, then I do a very basic shadow/lighting layer in order to get a color palette to work from. When I paint, in order to keep colors consistent (and work faster), I sample from the colors already on the canvas and just spread them around as needed to render the characters further and further. Eventually, after enough brush strokes, layer adjustments, and various special tweaks I do, you get what you see at the end there!
The reason I flipped the painting halfway through is because this commission is meant to symbolize progression, with Altairey graduating! Generally in cinematography, you want characters walking left-to-right when progressing, travelling, or growing. Why? Because that's the direction we read. That's how we subconsciously progress in stories. If you want the opposite (like someone backtracking), you make them walk right-to-left.