Moving tile and missing grout

cfth

I have 12X12 ceramic tile over the first floor of my home. It was installed over the foundation when the home was built in 1999. On the majority of the high traffic areas, the tiles make popping or cracking noises when we walk on them. I can actually feel movement when I walk on some of them. In addition, the grout is coming out in the majority of my kitchen area. What is the proper way to repair the problem before my tiles start coming out? Any guidance would be appreciated.

R&D Tile

I assume by foundation, that this is a concrete slab that they are over?

Either way, they all have to come up, there are many reasons why this could have happened, only fix is to redo the entire floor correctly.