any way to repair marble tile over subfloor
Natural marble is tough on a good base won’t hold up well at all in most cases with a substandard base. Since you have already started you might as well continue. Get a wider brick chisel this helps pop them off easier, that’s what I use like a Dasco Pro. If you stay with tile use a backer and use thinset to glue the backer to the wood then screw it down makes it much more solid base. If you have a air compressor here is where a air chisel can shine and pop the tiles really quick. I would verify that is tile below it looks like wood and may be the sub floor.  A better picture of the surface below may change the suggestion what year was the home built.