Tales From The Loop episode 7 tell the story of how George lost his arm and maybe even a brother.
Two of George's friends decided to pull a hilarious prank on George and leave him stranded on an abandoned island. Those friends are jerks.
On the island George gets bit by a snake and then encounters a creature on the island. It turns out the creature was a robot that his father created and then hid away on the island so no one would hurt it. Both George and the robot lose their left arms.
Later in life George learns the robots origin and builds up the courage to go back. Once there he finds the robot and befriends him offering his own robotic arm to the robot.