I do bridal clutches in my purse shop, and I've probably done more sets of five and six than any other number. I personally don't know that many people to have stand up for me at a wedding. :D
That being said, I offer sets in number from 3 to 6, with notes in each one that if they want more than six, to please contact me so I can sort that out. I did a wedding last year with 12 bridesmaids and 3 flower girls. O_O All I can assume is that either she was really popular or she had a HUUUUUGE family and everyone had to be included.