Any idea on what it would take to reno these FPs?

[Hassin Bin Sober]

18. I started to type that about the one by the stairs but I couldn't tell ...

… if that was wall behind the door jamb or the jamb itself.

If those are fake then all the better. Install some direct vent gas fireplaces on outside walls.

I would ditch those radiators and go with conventional hvac on the first floor - staged in the basement. Then maybe mini splits on the second floor or a small furnace and a/c with boxed in ducts in a soffit