Request #519 From Hope

I read this book in middle school and for the life of can’t remember the title or author. The main protagonist is a young woman I believe and her mum dies and her dad remarried to a mother who has 2 kids, the oldest is a young man near the main protagonist age and the second kid is a teenage girl. They live in a nice Victorian near a river or creek, that’s a little bit out of town. The stepmoms son came up with a plan to drug the parents with a spiked wine he has hidden so they can go out to the town and go party. The next part is a bit fuzzy but eventually the Son confesses to the main protagonist that he likes her and wants to run away with her and that his family is immortal. The protagonist rejects him, he somehow convinced her to get on a boat and he throws her off of it knowing she isn’t the best swimmer and hopes she just drowns, she somehow doesn’t and makes it back to land. The protagonist finds a shed with the proof that the son was telling the truth about them being immortal and the step mom tells her how they became immortal and then burns the proof. At the end of the book the Stepmother and son tries to run away so they can start a new life leaving the teenage girl behind but they end up in a car crash and dies. So the protagonist is left with this poor girl who lost her family and will forever be stuck as a teenager, but the protagonist steps up and takes care of her and left a note for future generations to know to be kind and patient to the teenager and to take good care of her.