Cleaning Edwardian tiles found under more recent tiles
I did something similar on a smaller area.

I used some plastic tools - scrapers etc and some cement remover product.

The cement remover product has an acid base (stings like xxxx if you have an open cut...), but I only applied it to small areas (used a cotton bud) and never to the joints between the tiles you want to keep.

If you don’t have patience at the beginning - you will by the end. And persevere with care.