This is really good! You should be proud!
From the looks of it, just by looking at it, I would say to try and try to make those shadows a but more pronounced. It looks like from where the position of the sun is, and how the bodies are positioned (especially the lioness), she should have a bit more shadow where the sun is not touching her.
But then...is this a sunset, or a sunrise? Cause you're going to have different kinds of light. I feel like you'll see more yellows in a sunrise, and more darker oranges and purples in a sunset. (Correct me if I'm wrong, please! LoL)
I would almost suggest using this scene from TLK 2 as reference for a sunset scene: Link, since the photo is WAY too big to put on here nicely.
In regards to a sunrise: Link
This is really the only example I have, unfortunately. I just wanted to show how more of the body was shadowed off if it was facing away from the sun.
This seems long, but it's really just a color adjustment suggestion.
But it looks really great! Their faces are lovely, I still have problems drawing them facing away from the viewer at an angle, but the male face looks great!