While I know Sylvia has made wrong predictions in the past, all psychics have. It is not an exact science. The future is not carved in stone. For the most part, psychics can only see the most likely outcome. All of the greatest psychics in the history of the world have been right a large percentage of the time. But ALL have made incorrect predictions.
Sylvia Brown is a Gnostic. Jesus and Mary were Gnostic.
This is fact. After the Death of Jesus, Mary moved to southern France where she formed the Gnostic Religion of the Cathars.
You can watch the movie "Bloodline", which shows an alternate view of the history of Jesus and Mary.
You can watch it in full length for free if you are a member of netflix.com.. Just type in search box "Bloodline" and watch in full length. If you don't use netflix, you can watch for free on youtube in 10 minute sections for free.
But to answer your question about the "twin" of Jesus she was referring to Didymos Judas Thomas. Judas Iscariot.
Judas was Jesus' most trusted disciple. He did not Betray Jesus, but carried out his wishes to the death.
This is pointed out in one of the greatest discoveries of all time..... The Gospel of Thomas.
The Catholic Cartel was able to keep this mostly secret until the discovery and translation of the Gnostic Scriptures found in the late 1940's.
If this is of interest to you, and you would like more information, you can start your journey at http://www.gnosis.org