Atticus is cute, but I honestly don't think it works with Kenneth. Any chance he'll go for Kenneth as a MN for a different name?
Yes, Calvin & Harrison sound odd together because they end with the same sound. Some may like it, but it's not a combo I love.
Maybe, though, Calvin Harris? Drop the "son" part? I think that works. Can't say I love it, but if it's a tribute to family names you like, would it help?