I like Casper/Kasper, and were really considering it for my son (I even called him this name for a few weeks while pregnant). I don't think the surname or his brother's name are any problems. I like Caspian as well though, maybe that could be an option?
Let us step into the night and pursue that flighty temptress, adventure.
PNL: http://www.behindthename.com/pnl/45898
Top: Alice and William
Bottom: Kensi and Alvin