I want my image to show two sisters, one and the other , with their backs turne

I want my image to show two sisters, one and the other , with their backs turned as if they were entering a light blue portal-type door. The 15-year-old sister has long wavy hair down to her elbows and is wearing a water-green dress that reaches below her knees, and the 13-year-old sister has long, straight hair down to her elbows and with bangs she has a pink dress that reaches below her knees. Both have dark brown hair and the sister is smaller than the 1., I would like my image to look like it is for the cover of a story called The Secret Door but the title is in English.