If Timmy isn't Rashel's brother, Then what is he to her? If he's just an Childhood Friend, then where was his family after his supposed "death"? Rashel never makes any mention of whatever connection he had/has to her other than that "Her mother told her to look after him".
Since Timmy supposedly died on Rashel's fifth birthday, it's possible that Rashel's mom was simply babysitting Timmy so he could be part of Rashel's big day. We probably don't hear about Timmy's family afterwards because Rashel is still very young and focusing more on her own grief than anyone else's, and even ends up going on the run after Hunter Redfern murders her great-grandmother in a house fire. As for why Rashel never reached out to Timmy's family afterwards, she was drifting through the foster system leading up to The Chosen and probably thought some harm would come to Timmy's family if she reached out to them.