Question regard ending C of clock tower: rewind

Hello! I just got the C ending, and this is the first one I've ever got. However, I really don't understand what it was about. When I got the the second floor with the elevator, Mary was pissed at me for killing Dan, and I ran away to the clock tower, and killed both her and Bobby. But I don't understand some things. Who the hell is Dan? I played the game with attention, but I didn't get any details about why Mary wanted to do the ritual, why she killed all of us, who is Bobby, why Mr Barrows is locked in a cage and purple (I gave him ham!). Also, there was a thing that I really didn't understand. At a point in the game, Jennifer used a pipe to uncover a secret room. The room was white and empty, and I couldn't explore it because Bobby decided to spawn, and I didn't return there. but I was pretty sure it was empty and the cursor didn't show anything to interact with. What am I missing to fully understand the story? Thanks!