So far we've seen about 4 of Big Mom's crew members (apart from the fodder looking members shown in one panel): the 2 guys on fishman island, the 3-eyed woman, and the 3-faced guy delivering the message about Fishman Island to Big Mom.
What I'm trying to get to is that they all seem like odd creatures. Could it be that the crew consists of strange creatures? Tamago says in this chapter, http://www.mangareader.net/one-piece/651/7, "and the beasts of Big Mom's pirate crew". Maybe they're known to be beasts.
Could Harpy Mone also be part of the Big Mom crew?