If there are too many coincidences in your book, just call it Magical Realism!
Lily is the responsible, sensible one in a family she thinks of as completely dysfunctional. Her father left before she was born; her dreamy, unsettled older brother is estranged from the family after a fight with their short-tempered grandfather; the grandmother is normal enough except for her imaginary friend… and Lily is tired of being the responsible, sensible one. She decides that she wants to fall in love.
Her grandmother, meanwhile, wants to repair the rift in the family for at least long enough to have a celebration for her husband’s 80th birthday.
The story is told from a number of different viewpoints as it develops, bringing all three generations into an improbable series of symmetries, synchronicities, and coincidences. If you can suspend disbelief about them, it’s a lovely, charming, book – and more than that, those symmetries are so beautifully constructed (for example, in the way that both young women are horrified to discover they resemble the male authority figures in their lives).
But I’d be hesitant about giving this book to a teenager. It feels too delicate and studied, and at that age I really didn’t want to spend time reading about old people. It is definitely a book about Lily’s entire family, and it almost seems as if Lily herself (the only YA in the cast of characters) get short shrift.