Er - well the whole concept of a family crest is not exactly cosher.

Just because someone with the same or similar surname had a crest at one time doesn't mean that anyone with that name is entitled to use that crest - and the original 'owner' might be using the crest due to some reason other than their name anyway.

I believe that some appointments brought an award of arms, but they were not heritable, so just because an ancestor might have had a crest during his lifetime, the right to display them died with him.

I have a huge book on heraldry somewhere - can't see it at the moment, I'll have to see if I can locate it - it can't be far away, no one would carry it any distance voluntarily....