Kellerbier is somewhere between a Helles and a Bock, normally unfiltered (which more homebrew is anyways, but this means you would disturb some of the yeast on purpose when bottling/kegging). Should be served warmer than most beers and with low carbonation levels.
(original explanation said between a Helles and a Maerzen, but that was a brain fart)
Urbock is... complicated. Some places call their Helles Bock Urbock, some call their Dunkelbock Urbock. I was thinking along the lines of Aecht Schlenkerla Urbock, which is their darker beer. Very smokey, smells almost like bacon.
Good luck! I would love to do this, but I am still working out my recipes (though my Helles that just finished is probably the best beer I have ever made! which isn't saying all that much, but still!)