EWTN Catholic Q&A
Question from Nadine Feery on 12-27-2012:

Did Jesus have brothers and Sisters? Is it a big deal if he did or didn't? Are they considered saints if he does??

Answer by Richard Geraghty on 02-17-2013:

Dear Nadine,

The Church teaches that Christ had no blood brothers or sisters. If one rejects the authority of the Church on this point, one is on the way to rejecting this authority on many other points. In doing that, one is no longer a Catholic in the eyes of the Church. That is the big deal.

Dr. Geraghty