I haven't followed th show very much, so I don't know if this had been mentioned before.
It is a fact that there are 3 sets of twins. Adria and Natalie we know about. Then there is Drew and Ben, and Diane and Lindsey. It appears that the remaining 2 twins might also enter the game. That could be the reason why there are 3 empty spots on the CBS site.
From what I found at another site, it appears that Drew/Ben have already been switching in and out of the game as well. Drew has moles on his chest while Ben doesn't.
click here for some proof
With regards to Diane an Lindsey. Diane has a mole just under the collar bone and Lindsey doesn't. Lindsey has a mole on her lower chin.
check out her site