Mentally write that off right now. The likelihood of that being usable after having been tiled over is very low. Brute force and a sledge, with a floor scraper, and all manner of PPO and home protection from dust is required. Zip walls, air scrubbers, goggles, gloves, long sleeves, etc.

They've been on there for about 10 years and are flat so I'm thinking the contractor may have screwed in some cement board and installed the tile over

I'm hoping that makes the removal easier and not as destructive

No idea without starting the process. I had one house where they screwed the cement board to the hardwood. We pried up the cement board then removed the screws. I had another house where they glued and screwed the cement board in place and all layers had to be cut out. It was a nightmare.

+1 for Hallett's answer.

Is is a wood framed house? If so, pounding the tile surface with a large hammer could cause the tile to break loose as the wood floor flexes.

Smashing is the least expensive way. If, you have a decent air compressor. A air chisel will make quick work of it. Cleaner than smashing.