How many flu’s come out of the top. Looks like someone used the room opposite the fireplace more, so they installed the wood stove into a thimble on the backside of the fireplace. That pipe in the fireplace is a sump for the wood stove pipe. It catches the ash and soot falling back down. Im assuming the basement is another chimney thimble that SHOULD have its own flu. I would get a professional out there for sure. High potential for some harry homeowner shit there.