Jesus, I would get some poll jacks under that asap. Dont try to lift it, just hold it in place. The floor probably won't handle the entire load. I think your going to need some professional help with this one I think. I mean if you really love that fire place I would be tempted to just anchor it in place where it is with 3 6x6s and some nice big wide fat footings. You may also want to consider just getting rid of the fireplace. They cause so many issues, next you'll be redoing the roof because its leaking. But that's not cheap either. Trying to lift those things sketchy, but it's also super sketchy now and it would be all around better if it was entirely vertical again. Hard to say what's best