Lost & Found (2016) on Netflix

Plot summary

Andy Walton swims well enough to dream of a scholarship, but he loses a contest and is caught stealing drinks from a store, so his parents send him and his younger brother Mark, who has a serious ear condition, to an uncle they have never heard of. Andy takes along a pocket watch he finds. Trent takes the boys to a remote island that once belonged to the Waltons, where their grandfather, World War II veteran Alexander Walton, vanished and the family lost the island. The West Forest is said to be haunted by the deaths of nine people. Andy meets Claire, whose father, John Broman, now owns the island and won the family's house from Trent in a poker game. The brothers learn that Alexander left a treasure for his family, and Andy is eager to find it.