The fact that your great-great-uncle pronounced the name differently is probably not related to the etymology. Many people have seen names in print and decided to give them to their children without knowing the original pronunciation, and so have ended up using a pronunciation different from the usual one. For example, the actor
Ian Ziering pronounces his first name to rhyme with the normal English pronunciation of lion or
Brian, not "EE-un" as is the normal Scottish pronunciation, because his parents just saw the name and assumed it rhymed with
Brian.