Hmm, for Matt, how about something straightfoward like "Tawny". For Harry's nickname, "Shadow" would fit, but methinks something ike "Knightgard" would sound good and fit his personality. I'd suggest just plain "Knight", but that's been used already.
Definitely an interesting Christmas holiday for all concerned. It'll be interesting to see what the second semester brings.
Author's response
I'm actually right now torn between Murgatroy and Hellcat, I'm loath to use Tawny, as I considered it at one point but I was reminded of a pornstar or stripper on the Maury Povich show named Tawny Peaks.