Between the Lighthouse and You, by Michelle Lee

Alice doesn't believe that her mother is dead.  There was a boating accident, but the body was never found.  And as she researches the circumstances of the accident, she discovers something else:  the Aviles Islands (where the accident occurred) are a magical place.  The inhabitants believe that once a year they receive messages from their departed relatives, which appear washed up on the shore.  These "tidings" are the responsibility of the lighthouse keeper to collect and distribute to the intended recipients.  When she disappeared, Alice's mother was in the process of investigating the myth.

Now Alice wants to return to the islands and interview the family that runs the lighthouse to see if she could somehow receive messages from her Mom.  While her family is unsupportive, her father does in the end agree to go down to the islands for a visit.

Leo is just the eldest son in the crazy large family that lives at the lighthouse, but he bears a heavy responsibility.  While the whole family claims to love the Tidings, Leo feels like he's the only one who appreciates their true meaning.  When he receives a special message on a cassette tape from his dead grandfather, addressed only to him, he must find a way to listen to it (this involves a bit of an adventure in finding a player).  When he eventually gets to listen to the message, he is surprised to find it is addressed not only to him but to Alice's family as well.

With subtle and unobtrusive magic elements, this middle grade novel is really about grief and recovery.  Both protagonists are learning how to adapt to a world where their beloved family member is gone.  In doing so, they find their relationships changing with the adults and siblings around them.  I found the siblings overly obnoxious, but portraying them as such allows for a clearer lesson that one must love the family one has in order to honor the memory of those who are no longer with us.