During Jesus’ earthly ministry, His earthly family, His mother and brothers, did not accept Him as the Messiah. At one point, they even thought He was insane and tried to take Him into care (Mark 3:21). But this does not mean that Jesus’ family were enemies of Jesus in the end.

After all, after Jesus’ death, Mary found refuge in the home of John the Apostle (John 19:26-27). Why she did so rather than living with her other sons is not known. After the resurrection, Jesus apparently appeared to His brother James (1 Corinthians 15:7), and James became a leader of the early Christian church (Acts 15:13) and wrote one book of the New Testament. His other brother Jude might also have become a follower (Jude 1:1), and it is said His brothers (Acts 1:14) were part of the early church, although that need not imply that all of the brothers became believers.

Therefore, it is not known when Mary and Jesus’ brothers came to believe in Jesus. Perhaps it was after the resurrection when Jesus appeared to James (but apparently not to Mary). Perhaps it was when Mary heard John’s account of the resurrection. Perhaps it was earlier. We just don’t know.

God has no grandchildren. Being related to Jesus or to other Christians is no guarantee that one will be a follower of Jesus. But it is no barrier to following Jesus either.