Bernard=Brian???

Good Morning !  I am looking for advice.!

Is Brian some derivation of Bernard?  I have three adults who I am fairly certain are siblings, yet upon finding their birth records, I see that two children have a father of Brian, but one child has a father of Bernard.  Are the two names somehow equivalent or am I stuck with three people who aren't siblings?  Or should I guess that this was an error in transcribing? I am guessing that it isn't a case of two husbands.  The Bernard child is in the middle.

I welcome your advice and I value your opinions.

Thank you in advance.

Barbara

:-)