FSIL question- help

My FH is from another country (Israel). They don't have bridesmaids in their weddings, but they know about them from watching enough American TV. I invited the three sisters so be my BM. Two of them don't like the derss (it strapless and they are busty, kinda tomboys and self conscious), and I am waiting for the youngest sister (15) to weigh in about the dress. I told the other sisters just to wear something in the same color and to march down the aisle and they will stand on FH's side. Does anyone have any other suggestions of how to handle this?

I am not insulted that they don't like the dress. The 15 year old is really judging this on the dress- but thats OK- she's 15. But I just can't imagine his sisters not being in our wedding just because they don't like the dress.