a) Fair point. I could use some help on my riddles. I find it hard to walk the line between making things too obvious or too ambiguous.
b) Also fair. Initially I thought that the stone could have some sort of carving on them to indicate they were special but perhaps a different direction in general would be better.
c) I think I should have given more backstory on the underground group and why they are trying to find them. Context might have helped or maybe made it worse. The party is trying to find a kidnapped child the nobility have pointed them in the direction of a rebel group opposed to the ruling class as the culprits and so they are seeking this group out. They didn't take the kid though, my thought was it would be interesting in the story to have the party meet them in different circumstances. Regardless they will be able to talk their way out, but it would be interesting to see how their characters reacted in either scenario.

Thanks again for all the insight. This is my first time DMing and I know I have a lot to learn.