A long-sleeve dress and pants set for a 12-14" doll might typically include the following features:
Dress:
Long sleeves to provide coverage for the doll's arms.
A fitted bodice  and a  gathered skirt that falls  below the doll's knees, providing a modest and stylish look.
Closure at the back with  Velcro, for easy dressing.
Pants:
 elastic waistband and legs to ensure a secure fit.
Made from a coordinating fabric to complement the dress or to create a matching ensemble.
Overall, the dress and pants set for a 12-14" doll would offer a combination of style, comfort, and quality craftsmanship to enhance the doll's wardrobe and provide endless opportunities for imaginative play.