Robert Pattinson and Kristen Stewart have set aside all their differences and are finally happy again, but Pattinson's sister, Lizzy doesn't seem happy the reunion after Stewart cheated, reports The Sun.

Pattinson is back in south-west London for holidays with his family while his girlfriend, Stewart, is in LA. Lizzy, Pattinson's sister took this family time to give his brother some advice and express her disappointment for taking back Stewart she cheated on him 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 told the Sun. "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."

Stewart has not been in favorable terms with both Pattinson's sisters, Lizzy and Victoria. They had warned their brother not to take Stewart back after the highly publicized fling with Sanders.

"Don't even think about getting back together with Kristen Stewart!" they said, according RadarOnline.com exclusive report, before Pattinson got back to Stewart. The two Twilight stars came together during the premiers of "The Breaking Dawn- Part 2" and source revealed Pattinson's mother seemed to have forgiven Stewart.

 "Kristen and Rob's mom hugged when they saw each other at the after-party. They looked really happy to see each other and spent quite a bit of time talking and laughing. Bill Condon and Rob were also there, but they were talking to each other, and Kristen and Rob's mom were talking to each other," a source told Hollywoodlife.com. "Kristen and Rob's mom looked like they have a great relationship. I didn't see any tension between them whatsoever!"