I don't know, but so others can best advise are they ceramic, porcelain, or something else? Thx

There are ceramic..

Since th

Since they very old we wanted to remove the white stains before sealing them with a clear coat, which will prevent future stains. Now they have different colors

They look like they might be Saltillo or similar terra cotta tiles. If so, cracks and chips are likely to be difficult to repair. I'm facing a similar issue with some of mine. You might try scrubbing the surface with a green fiber pad and household cleaner to remove any residue, wipe with a clean damp cloth to remove the cleaner, let dry, then apply a clear sealer made for terra cotta. The sealer may help camouflage the damage by darkening the light spots. Try it first on one or two tiles in an out-of-the-way location.
(Oops, posted that before you said they're ceramic.)

This is NOT my field, but as these being very old ceramic tiles, my thinking is that they aren't white stains persay, but rather natural wear and tear in where the manufactuer's color worn off revealing the white underneath.

The first picture looks like Saltillo, the second like ceramic. If they are ceramic you can't really repair them.

@Makaloco thanks a lot for the advises. We have tried to use liquid soap and a gentle abrasive sponge but the result is even worst then expected. These tiles are not terracotta but look like them. They stain very easily, we tried to had baking soda in the water to clean them and that helped a bit but the major stains are not coming out. Nothing we know as worked yet still hoping to find the granma receipe for them :)