Loose tile & hollow Sounding Coping

All,
I have a couple of loose tiles on my spa wall 2 feet above the water line where they meet the coping. The grout where the coping meets the tile is gone, which I imagine contributed. My question is this. I would like to just re grout where it is missing and hope it lasts for a while. The pool is only six years old and I don't fee like replacing tiles at this point. Although, it would only be a few. I think I would rather wait until either they pop off or more get loose. I do have to re-grout at some other areas as well but no loose tiles.

Also, tapping on several of my brick coping reveals a hollow sound. Nothing loose, no mortar cracks in the joints. Here again, not loking for a major project at this time.

I would rather get another 4-5 years out of everything and then have someone come in to do the whole ball of wax.

Any thoughts or similar experiences?