According to the
Complete Guide to LnC Characters Jack and Denny's last name was "Miner". You can also check the script for Foundling at the top it gives a list of character names... Hold on, I'll double check it...
Hmmmm. The section of the script which lists out the characters (actors) needed for the episode doesn't list a last name. I guess it must have been mentioned at some point.
Although I've used Jack and Denny at various points in several of my fics I don't think I've ever used their full name.
