Charlie St. Cloud

Charlie St. Cloud is a sailor who wins a boating race on his sailboat, the Splendid Splinter, along with his younger brother Sam. He receives a sailing scholarship to Stanford University. Charlie graduates from Winslow High School and after returning from his graduation ceremony, Charlie promises Sam that they will practice baseball every day until he leaves for Stanford. That night Charlie is supposed to go to a graduation party with his friends, but his mother makes him babysit Sam while she picks up another shift at her job.
When Sam watches television, Charlie tries sneaking out to the party. He is caught by Sam, who asks Charlie to drive him to his friend Tommy's house. Charlie and Sam get into a car accident. During an out-of-body experience, Charlie hugs a badly wounded Sam and reassures him that everything will be fine.
Knowing his injuries are fatal, Sam asks Charlie to never leave him alone, saying that if so they will always be together. As Charlie promises, a paramedic named Florio Ferrente revives Charlie; Sam has died in his arms. At Sam's funeral, Charlie runs off after being unable to put Sam's baseball glove in the grave. After a run through the woods, Charlie finds Sam's spirit and discovers that Sam can interact with him on the physical plane. Charlie fulfills Sam's dying wish by practicing baseball with him every day at sunset.
Five years later, Charlie, who gave up his scholarship, is a caretaker at Waterside Cemetery. During a trip into town, Charlie visits the boat docks and meets Tess Carroll, a sailor planning to sail solo around the world. The following day, Charlie runs into Florio. Florio is dying of cancer and asks Charlie if he ever wonders why he was saved. Charlie returns to the cemetery and finds Tess injured tending her father's grave. He takes her to his home to patch her up and they develop a relationship. Sam begins feeling that he is being erased from existence because Charlie is forgetting him when Charlie arrives late for their game. Tess follows Charlie and he explains to her that the more he is in her world, the less he is in Sam's.
Charlie discovers that Tess went missing while sailing through a storm a few days earlier; Charlie has been seeing her just like he can Sam. Florio's wife Carla tells Charlie that Florio died the previous night. During one of the evenings Charlie and Tess have together they play hide and seek. Tess sticks a note on the door which says "come find me" with a drawing of a boat beneath it. Charlie realizes that Tess is not dead and that he must find her.
Along with his friend Alistair and Tess's coach Tink, Charlie takes a boat to find her. The following sunset, Charlie misses his game with Sam. As Charlie confesses his love for his departed sibling, Sam tells Charlie that he loves him back and moves on from the living world. He appears to Charlie as a shooting star in the sky to reveal Tess' location. The group finds Tess' wrecked boat along with her lying on the rocks. Charlie uses his body heat to keep Tess warm until they are found by the Coast Guard.
Alistair tells Charlie that Tess had hypothermia and he saved her. Later, Charlie purchases an old boat and asks Tess if she would like to take a ride with him. However, Tess fears him explaining that she had vivid dreams about them together. Charlie tells Tess that her dreams are memories and recites a quote from her father's funeral that they spoke about in her dreams. Charlie resigns from his job and goes into the forest to say farewell to Sam, telling him they will always be brothers; although he is unable to see him, Sam is there and reveals that he is at peace. Charlie and Tess sail around the world.

Question: What is the relationship between Charlie and Sam?
Answer: Brothers