Centre Tonga'uiha, who has 24 caps for Tonga and made nine Premiership appearances for the Exiles in their debut season in the top flight, joined prop Bateman in extending his contract with the Oxford-based side.
Welsh head coach Lyn Jones told the club's official website: "I'm absolutely delighted that Hudson and Greg have committed themselves to London Welsh.
"Hudson has really stepped up to the mark this year and has thrived in the Aviva Premiership. Greg has grasped his opportunity with both hands and is evolving into a decent Premiership player with the potential to go further.
"These two re-signings signify the ambitions and long term objectives of London Welsh RFC."
Bateman said: "I've improved a lot in my time here and I'm looking forward to what I can achieve in the future.
"Lyn's worked a lot with me on areas of my game where I can improve and I take that very seriously. I want to push to be involved in the first XV more and more."
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