Okay, an active cave is one that has all the pretty white formations everywhere basically.  And active cave is still growing.  It is being supplied with the proper amount of water flowing down its formations.   It is a “live” cave.  
Wolves don’t really live in “caves” in our world, they live in dens, or what we cavers call bum caves (they don’t go anywhere and they’re very earthen rather than rocky).   Bear do live in caves, but not in Mo. Anymore, although we can sometimes still find their dens.  
However, you could probably put wolves in your cave and no one would know any better.  Besides, it’s fantastical, you are allowed to divert from reality 

 .  The only thing I would be sure to mention about a cave with such creatures would be that it is more flat bedded and has craggy crack type passages.  If you have a cave with a lot of shelf stone then the wolves can’t travel very well and it defeats the scary aspect you want to create because the humans could just climb up the rock face onto the shelf stone.  
A breakdown passage is exactly what it sounds like.  The rock has broken down over time.  In a breakdown passage there are huge chunks of loose rock everywhere.  They can be very dangerous, depending on the placement of the rock.  It often times looks like a big pile of rubble and generally scales upwards like a little hill you have to climb over.  Sometimes, in large passages, this breakdown can be tremendous and it is a very large mountainish climb, just depends.  Sometimes when you get to the top of a breakdown passage the passage has been choked off and so you will carefully have to move some of the rubble away to continue on.  But not all Breakdown rooms lead somewhere.  Some just end.
I think the narrow fissure is possible.  However, you’d have to have some skinny MC’s if they can get through and not the wolves.  Wolves are able to contort their bodies very easily, so they could make it through some things that human’s can.  My thoughts would be to do a shelf passage maybe inside a narrow cleft.  
Hope that was helpful.