I prefer
Bruce because it reminds me of
Bruce Wayne (Batman!) and I think the nickname Brucie is really cute, however I'm aware some people might have "pet-zoned" it or think it as thuggish. I don't hate
Graham but all the ones I have known are over forty, possibly over forty-five so I consider this to be old and slightly dated.
I think
Bruce sounds better with the middle name
Mitchell however
Graham and
Audrey sound more likely as siblings than
Bruce and
Audrey do.