Prop Vea has signed from New Zealand side North Harbour, while centre Helu has previously enjoyed a spell with Bristol, and Young has talked up the prospect of the two internationals playing for the club.
The 45-year-old told the club's official website: "Both of these players will add important depth to the squad.
"Taione is a developing prop and he joins a group of young front row players here who are all pushing each other very hard.
"William is a hard running player who covers a few positions in the backline and we're looking forward to their arrival."
Wasps begin the new Aviva Premiership campaign with a home fixture against Harlequins.