[pushkins]

No you can use the pressure treated ply for the first layer of sub floor then screw to that a layer 5/8" sheet of Advantech, just as strong and made for floor adhesion and for the application you need.

If you still want to use the double layer of CCA/CCQ then add a 1/4" layer of flooring ply before you lay the peel and stick tiles.
Don't forget though you should also use a "primer" before you lay the tiles, you can get it in any of the bog box stores in the flooring department.

There is no real reason to replace the "cross members" around the toilet flange, the floor joists and the "double" layer of floor sheathing is way more than enough.