It’s very unlikely that all your bridesmaids will be exactly the same shape and size.
A girl that wears a size 16 wont look the same as a girl that wears a size 2. (especially if she’s busty!)
You should either choose a dress that will flatter the largest girl or let the bridesmaids choose their own dress but stick with the same color, designer and fabric.
Be sure that no one picks the exact same dress and that all of them are hemmed at the same length.
If you do this, you will make everyone happy and save the girls a ton of money in alterations.