Would this be too much to put into one story?

i want to write a story but I'm wondering if this is too much/ too busy for one novel. It's not supposed to have multiple novels for it,.

It's about a teen girl who has died and went to Heaven and was told her little sister would join her soon, so the teen,Kurisu escapes Heaven Because Kurisu is socially awkward she talks Itsuko into coming with her.

Itsuko's organs were donated when she died in a car accident due to a "will" Itsuko left . Itsuko had a friend named Jun who needed a heart transplant which is why Itsuko made that will. Her older sister Chihiro now holds resentment towards Jun and Lia, who introduced Chihiro and Itsuko to Jun. When Itsuko arrives back on Earth she will see the good and the bad that her will left. (Her other organs went to other people, she'll meet some of those people.

Kurisu and her little sister Mayuri were in a fire and Mayuri's body was comepletely burnt but she was still alive. Kurisu was brain dead after part of the roof of the burning house collapsed on her head but her body only suffered minor burns. Both bodies were recovered and in a last ditch effort to save Mayuri they transplanted her brain into Kurisu's body. This procedure is very new and doctors knew it would only keep Mayuri alive for a year before the body rejects the brain (Until then they'd use a treatment that allows the brain to trick the body into working for it be the ttreatment is temporary.Mayuri knows but Kurisu does not is this to much to put in a book thanks