Actually I don't think Eric (America's Player) is counted as a "Mole" since he was a housemate and eligible to win the grand prize. Moles in BB generally are meant to stir up the house and the Mole isn't eligible to win the grand prize. Eric is just classified as a housemate with public controlling his moves. Pinoy Big Brother: Teen Edition Plus also used the idea but used guests instead of housemates (for this edition they were named House Players).
Also BB9 USA was not the first BB to have joint housemates, BB5 Australia was with the Logan twins. However BB9 USA was the first to feature strangers as joint housemates except for Jacob/Sharon. BB9 USA was the first season in which the entire house was made up of joint housemates though.
I said "coupled". I think the first "joint housemates" would then be Adria/Natalie (USA 2004), since for the first four weeks they were the same housemate.