Well done you.
A grinder I guess. You need to somehow smash the
tile up gently. If that can happen. Break the tiles. Grind into them. If you have a depth guage on a grinder you want to use that and just grind strips down the tiles so they become lots of small parts of
tile. Then just chisel them up, sort of.
It's going to be a maul. Not going to lie to you.
Then once you have got the
tile up. A Fein Multimaster with a rough rasp on them would get the adhesive up. Might be worth the tiler doing this he should have the tools or access to them perhaps.
Hire shops might have some of of what you need.