Sketching out the 3 sisters, each on separate layers in different colors to edit and distinguish as need be.

Line Art

Each inked on a separate layer, adjusted the middle sister's face to age her up a tad.

Base Colors

I put hair colors on one layer, skin colors on another layer, clothes on the final.

Coloring Skin

The basic steps for skin, I also follow with other layers

Color Rest

Following Skin coloring technique I color the remaining layers, ad details like clothes patterns, color line art to soften the look.

Finishing Up

Added a background and a texture overlay to give it an even softer look and aged appearance.