A few questions about my DIY tile project on the spillway

Hey there. I am hoping someone can help. I am an avid do it yourself-er, but am new to the pool world. I have a pool that is probably 30 years old. It has the original tile on it, which for the most part is in good shape. The waterline is great, but there are a few areas around the hot tub that are not. One half of the top edge between the pool and spa is pefect, the other was loose, got stepped on and then it went down from there. I was able to pry up the tile with my hands, no chisel. I planned to pull them up, match the tile as close as possible and then just re-tile that section, but when I lifted up the old tile, it appears to be on a mud bed that is two inches thick. On one section, the mud bed is not completely flat and without flaws, but it is pretty good. On the other section, half of the mudbed came up with the tile. So, my question is, what do I need to do to prepare this spillway for new tile. The two areas where the water spills from the hot tub to pool are actually O.k., but as long as I am doing the whole top, I might as well do the whole thing. My concern however is that when I pull off the lower spillway pieces, that I will lose the fascia of tile between the lower pool section and the upper spa section.

I am not only new to pool repair, but to forums as well, but I sure could use some help. I can send photos as well. Can anyone help me.