The best option for your bridesmaids might be a skirt and top. Here is a selection of sewing patterns for modest long skirts, that are specifically designed for special occasion fabrics such as satin, taffetta, georgette, chiffon, crepe, and crepe de chine.

Chardonnay Skirt by L. J. Designs (XXS-4X). Simple to make skirt with front cascade. Suggested fabrics include silk, poly silkies, burn-outs, and sheers.
Simplicity S9016 Misses’ Asymmetrical Skirts. Asymmetrical skirts in various lengths, with high-low hemlines. Suggested fabrics include crepe, double georgette, and silky types.
New Look Sewing Pattern N6605 Misses’ Skirt with Neck Tie. Skirts in various lengths. Suggested fabrics include double georgette and silk types.
Simplicity Sewing Pattern S8885 Misses’ Skirt and Pants. Skirts in two lengths. Suggested fabrics include crepe, double georgette, satin, and silky types.
Simplicity Sewing Pattern S8868 Misses’ Overlay Skirts with Top. See views A and B (skirts). Suggested fabrics for overlays include chiffon and organza. Suggested fabrics for linings include crepe de chine and lightweight satin.
New Look Sewing Pattern 6580 Misses’ Circle Skirt. Long skirt with optional overskirt. Suggested fabrics include charmeuse, crepe, jacquards, and silky types. Suggested fabrics for overskirt include lace and novelty sheers.
Burda Style B6386 Misses’ Full Skirts. Ankle length skirt with front pleat. Suggested fabrics include satin.
Simplicity Sewing Pattern S8743 Misses’ Pleated Skirts. Floor length pleated skirt. Suggested fabrics include brocade, satin, and taffeta.
New Look Pattern 6400 Misses’ Skirts in Various Styles. Skirts in multiple styles and lengths. See view D for the longest skirt. Suggested fabrics include crepe, crepe de chine, jacquards, and satin.
Simplicity Pattern 1069 Misses’ Wide-Leg Pants or Shorts & Skirts in 2 Lengths. See View D floor length wrap skirt. Suggested fabrics include crepe, crepe back satin, and double georgette.
New Look Pattern 6287 Misses’ Pull on Skirt in Four Lengths. See view A. Suggested fabrics include charmeuse, crepe back satin, and silky types.
Simplicity Pattern 1616 Misses’ Knit or Woven Skirts. View D is a long skirt for woven fabrics. Suggested fabrics include crepe de chine and double georgette.
Kwik Sew K3381 Misses’ Tops and A-Line Skirts. Skirt B is a long skirt. Suggested fabrics include jacquard, taffeta, satin, crepe, and silk types.
Vogue V9173 Misses’ Floor-Length Tiered Skirts. Long, fancy skirts. Suggested fabrics include shantung, satin, taffeta, and lace.
Butterick B5431 Misses’/Misses’ Petite Bias A-Line Skirts. Ankle length and above ankle options. Suggested fabrics include georgette, lightweight crepe, crepe-back satin.