I do think it would fit with the sibset, but I personally can't get past the movie reference. You could always spell it
Kaspar (technically correct), but then you run into the whole kre8tive mess. Perhaps as a middle name, although I don't think the younger set has such a strong reference to the friendly ghost.
Casper MichaelCasper RupertCasper JohnCasper WilliamCasper Andrew
Owen CasperDavid CasperJohn CasperIan Casper