Australia prop Kaufusi, 26, has joined from Newcastle Knights while second row Rodney, has left Manly Sea Eagles to play for the Super League side.
"Shane is an experienced player with a lot of games under his belt including a Grand Final win,” Harlequins coach Rob Powell told the club’s official website.
“He is also a decent defender and will provide good strike on an edge."
"Antonio has been played some of the best football of his career this season. He is a big explosive prop and will add a lot to our pack."
The Quins are currently placed in 12th position in the Super League XVI.