Cracks in tiles. Since you said that some have a hollow sound when you
tap on them, that is NOT deteriorated glue or anything like that, it
is a lack of it. I wonder what kind of adhesive they used? Since you
have a concrete slab, they should have just used thinset mortar like
stuff. If you have tile in other places on the slab besides the foyer
and they aren't cracking, you might get lucky and the only problem you
have is a poor installation job. This happened in my new house which
is on a wooden floor, I have a crawl space. A majority of the tile had
to be replaced because they didn't use enough glue. The tiles will
crack when you walk on them if there isn't or mortar like adhesive on
the entire underside of the tile and the same thickness under the
tile. You will also see that the grout joint starts deteriorating from
the minor movement of the tile.
Its really hard to say if you have a slab problem. If your brick on
the outside doesn't have long cracks, many feet and there are no
cracks in the visible concrete footer/slab, then you likely don't have
a foundation problem.
What kind of soil do you have, is it clay?
Your house will actually shrink over time because everything it was
built with is drying out. If it is stick built, which I imagine it is
in Dallas, not much modular construction up there, then it was rained
on. All the 2x4's got wet. If they didn't dry real well before it was
closed in and drywalled, then the timbers are slowly shrinking and
voila, you have cracks showing up.
If I were you, I wouldn't call an engineer, at least yet. get the
tiles pulled up, heck, take a hammer and break them out your self.
Another excuse to buy another tool, I love those opportunities. Get a
2 inch wide brick chisel and chip away and clean up the adhesive on
the slab and look, do you see any cracks? If not, get the tile
installed correctly, fix the cracks in the walls with some drywall mud
and your index finger, watch for doors or windows sticking and live
life. Some may say you have to use drywall tape or mesh over those
cracks but if it were me, I'd go the easy route first with the spackle
and finger. You could use a pointed can opener and v-shape each crack
first so you can get more spackle in the crack areas, this would
probably be better then just trying to dab/force some in the crack.