A bridal party with mismatched dresses is acceptable as long as one or more elements of the dresses are complementary and each bridesmaid is comfortable with her choice. Choosing matching colors, lengths or fabrics are several ways to accomplish this.
To avoid confusion and disagreements later, make a preliminary appointment at the bridal salon and decide on the range of options from which the bridesmaids will be choosing. Consider selecting a single fabric, neckline or color palette while allowing each one to pick the style best suited to her body type and budget. It is generally a good idea to settle on a general or specific length in advance, as it is challenging to look complementary if half the bridal party is walking down the aisle in floor-length formal gowns while the other half has a hemline that ends above the knees.