Jacob is the son of the late Marshall Bowman, the half-brother of Grace Bowman and the adoptive younger brother of Tom Bowman. He is from an affair that Marshall had while he was married to Kathleen Bowman.
Jacob wants to come spend the summer with her (and possibly throughout high school) in California when she comes back so he can get to know his siblings.
At the end of the episode Suddenly Last Summer, Kathleen gave in to Jacob and said that he could come with them. She opens the door of her house and motions for him to come in after her, and it is not long after that particular moment that Grace came downstairs.
The episode ends with Jacob gleefully saying hello to Grace and Grace telling her mother that she'll be at Adrian's. It is unknown when Grace will accept Jacob as her brother.
Jacob ends up leaving the United States before school starts, returning home to South Africa, although it's never revealed why he returned home.