cut the caps.. we aint deeef ..
if the petcock is off and fuel still leaks, the petcock or the tank itself is leaking..
chances are the petcock is leaking .. fuel flows into the carb at all times AND the carb has a leak, so it gets on the floor..
track them leaks down and fix 'em. Clean everything spotless. Put a bit of fuel into the tank and observe closely.
you just got the bikes so give them a throrough going over.. get the 2 QT manuals on this page and read Fred's Guide at the top of that page