This is the ref i used so faar, as i will need other ref i will post it here as well.
Here is the the final sketch/linework.(i did clean it a bit) I did many version till i was halfway happy, so this is it for now. There is no need for clean linework because you will not see any in the final Image.
I want the final Image look more classic, so i will try to make soft lighting (sunlight + fire or candle light) Backround will be the brightest part, i will paint it later. The BG light will cast a bright light on the characters, i will do it in the last step. For now i will make only the ambient light, i will make it very basic with not many reflections or any refractions or transfluency effects. Not all Object will affect eachother by casting a shadow, this i will later.
First i cover the linework with a dark green layer, i paint from dark to bright and want some green tone in the shadows. i also make roung outlines with a more darker green tone, this will help me to separate the objects easier. I make the linework transparent so i don't forget to paint the dark spaces. As i will work out the details i will delete the line work more and more.
I Start with the girl in the middle as i like her ass, so bear with it. I choose a dark brown tone and add more brighter colour step by step. The importance is to pick different colour values to make the skil look more natural. (this you don't see here very well as i am still on the dark regions.
After i got bored with her ass i moved on to her face. I do not paint all body parts at the same time, that is not good but i get bored otherwise. you should try to avoid it, try to paint all connected bodyparts with the colour you are using before moving on to a brigher value, bacause you may end up with many different values and that will look like the parts don't fit together.
Using the colourpicker i do the colourin job on the face now, as you see i moved on much farther with the face instead of using the skin tones on the rest of her body or on the hands. That is because i plan to use her face as colourreference for the rest of the body, this way i may save lot's of work in a bad case. Bad case would be if i would dislike one of the colous and would have to change it everywhere.
As you can see i used different tones in the brighter values, this makes the skin look more natural.
!!! However this is NOT the final colouring for the face, this is just the ambient light. As soon as i finish the ambient light on all obejcts i will tone them down again, make them darker, then add other lightsources and work out details.
Also note that i do never use black for colouring, later when i will darken the ambien light the image will have black values in the darkest regions.
(the bright highlight on her nose and eyes is not part of the ambient light, but i couln not resist... I will remove it later again)
This is how i ot so faar, more updates will come!