I just went through this with some of my bridesmaids, as one has shorter hair. An easy thing for you to do would be to get some "bobby pin" type bling for your all your bridesmaids, as the ones with buns could stick these in their buns and the one with shorter hair could pull a few curls back and pin them with these. As for combs, it's difficult to say without knowing your friends' hair type whether these would stay. There is a method where you can take a section of hair and pin it in the opposite direction of growth in order to create a taut base for the comb, but it doesn't always work. Easier than a comb might be some blingy wing clips for your short hair bridesmaid.