“Branch, don’t be a baby. We’re your brothers.”
“And Poppy is the only family I have left.” Branch puts emphasis on her name, watching as they flinch back. “You don’t abandon family. Not that I’d expect any of you to know that.”
(or, alternatively, poppy gets taken by superstars velvet and veneer and it's a downward spiral from there.)
Branch was always alone ever since his Grandma died. Nobody was there for him, so he left but stayed close. Twenty years later, he meets Poppy and she makes it her goal to reintroduce Branch to Pop Village.
Branch had never expected this to lead to him saving Trolltopia and reuniting with his brothers.