ANSWER: Several New Testament scriptures confirm the fact that Jesus was NOT the only child born into the family tree that begins with Joseph and Mary (contrary to what Catholics and other denominations may teach). In fact, Mary gave birth to a total of at least FIVE boys and at least two girls (Matthew 13:54 - 56, see also 12:47)! Please see our article on how the New Testament shows that Christ did have brothers and sisters.
Accounts are sketchy as to what happened to Jesus' brothers and sisters in his family tree after His resurrection. The Bible does give us, however, clues regarding what may have happened to his mother Mary. We find when he was on the cross that he commended the care of his mother into the hands of the apostle John (John 19:26 - 27).
Jesus and John were highly likely relatives. John's mother (named Mary) who was married to a man named Clopas, was the sister of Jesus' mother Mary. This would make him and John first cousins. This, of course, begs another question as to where Mary spent the remainder of her life in the care of John.
In Raymond Capt's book, Traditions of Glastonbury: The Biblical Missing Years of Christ - Answered, the tradition is that John put Mary in the care of an uncle, Joseph of Arimathea, a rich tin merchant who sailed to Britain shortly after the resurrection of Jesus, settling in Southwest England in a village called Glastonbury. This tradition holds that Mary lived there with a few other disciples for 15 years then died. Tradition also states her death occurred in 48 A.D.
I could only find some information about two of Jesus' physical brothers, James and Jude. The Bible's New Testament mentions four men named James. The first James is the son of Zebedee and Salome (cf. Matthew 27:56 with Mark 15:40) who is the Apostle John's older brother (making him a cousin of Jesus). This identifies Zebedee and Clopas as being the same individual. The second James was a son of Alpheus, who was one of the disciples of Christ. It is not at all clear whether this is the same James as the one related to Zebedee.
The Apostle Paul wrote in 1Corinthians 15:7 that the first post-resurrection appearance of the risen Christ was to James who from that time forward gave the rest of his life to Christ. James was an early leader of the Jerusalem Church. The last Biblical mention of James is in Acts 21:18 where the Jerusalem elders exhorted Paul to take a Nazarite vow.
Jude, another brother of Jesus' family tree, also did not believe in him until after His resurrection. Jude is the author of the Epistle that bears his name. No more information exists about the two remaining brothers of Joseph and Simon.
The book of Matthew states that he had at least two sisters in the family named Mary and Salome. Parallel accounts in Matthew 27 and Mark 15 link Mary and Salome (Matthew 27:55 - 56).
Mary, mother of James and Joses, is considered to have been Clopas' wife (see John 19:25). Was she the sister of Jesus? This is a possibility. Salome was the wife of Zebedee and mother of James and John.
Are there people living today who are in the family tree of Joseph and Mary, who would be blood relatives of Jesus? Given that Mary had at least SIX children other than our Savior that (likely) lived to adulthood, there is a high degree of probability at least a few people living today have a genetic link to him. Thank you for your question regard our Savior's physical family tree!