We sometimes think of the Twelve apostles as a group and suppose that Jesus called them all at once. This is not so.
According to Mark 1-2, Jesus first walked along the shore of the Sea of Galilee and called Peter, Andrew, James and John—four fishermen, a homogenous group.
Then, after settling in Capernaum and doing some ministry trips to the surrounding area, He reached out to a whole new group of people—Levi and a group of tax collectors. Now fishermen and tax collectors, faithful Jews and servants of the Roman oppressors would not be expected to get along. But Jesus brought them together.
Perhaps the fishermen (at least, Peter, James, and John) formed Jesus’ inner circle because they had seniority—they were called first.
Since Matthew was a tax collector (Matthew 9:9, 10:3), it is often assumed that Matthew and Levi were the same person. If so, then Levi also became one of the Twelve (Mark 3:18).
One of the other apostles was James, the son of Alphaeus (Mark 3:18). He was also called “James the Less” (Mark 15:40)—perhaps because he was shorter or younger or less prominent than James, the son of Zebedee. In Mark 15:40, this James is described as the son of Mary, another of Jesus’ followers from Galilee. But Levi was also called the “son of Alphaeus” (Mark 2:14). If Matthew was Levi, then Matthew and James could be brothers, sons of Alphaeus and Mary. This would be a third set of brothers among the Twelve (along with Peter and Andrew, James and John). If Levi was not the same person as Matthew, James could still have been the brother of Levi and might also have been a tax collector; at any rate, he could have been part of the tax collector crowd.
Philip and Nathanael, on the other hand, appear to have been friends (John 1:43-51), not brothers, and they were from Bethsaida, the same town as Peter and Andrew (John 1:44). They had Greek names and may form a third group among the Twelve, that is, Hellenized Jews (Jews influenced by Greek culture but not necessarily working for the Roman government).
We sometimes think Jesus calls individuals, and He does. But those individuals come with their connections and baggage, their families and their friends. As it was with Jesus’ first followers, so it is today. When one person becomes a follower of Jesus, one result is that his friends and family members are often given an opportunity to become followers as well.