The actor, who spent Christmas in London, was warned by sibling Lizzy not to take his unfaithful Twilight co-star back, The Sun reports.
It was revealed back in July that Stewart had cheated on Pattinson with Snow White and the Huntsman director Rupert Sanders.
"The rows kicked off on Christmas Eve when protective Lizzy had some words with Robert about getting back with a cheat," a source said.
"They were out drinking in Barnes, where Rob grew up. Lizzy was giving him grief about taking Kristen back and said she's always hated the way he's been treated by her.
"He and Kristen spent the festive season apart partly because she's terrified of facing Rob's family."
It was previously reported that Pattinson had set a deadline of Valentine's Day (February 14) next year to make a decision on his future with Stewart.
Photo gallery - Kristen Stewart and Robert Pattinson's relationship so far: