This weekend I will finally start cutting & cementing the flagstone on
the walkway (see four photos below for detail) and three questions arose:

Q1: What is UNDER these flagstones on cement (are they glued?)
Q2: If you glue them, how do you keep the tops evenly flat?
Q3: Since the step width varies by 3 inches, can it take a 3" overhang?

Here is a picture of the concrete base that I plan on putting flagstone.
Notice the base starts at 18 inches but eventually narrows to 15".
Can a 3" overhang (maximum) be supported with just the packed soil below?
http://www4.picturepush.com/photo/a/...mg/7433812.jpg

Here is a picture of that same base, only further away to give you a
better idea of the problem set:
http://www5.picturepush.com/photo/a/...mg/7433813.jpg

Here is a picture of the enigma.
What is UNDER these existing flagstones?
Are they simply GLUED on? (There seems to be NOTHING under them!)
http://www1.picturepush.com/photo/a/...mg/7433814.jpg

Here is another picture of the existing flagstones in the water feature.
They appear to have NOTHING under them. Can that be?
http://www3.picturepush.com/photo/a/...40/7433816.jpg

The reason these three question matter is:
a) I need to lay the flagstone on the concrete and I don't know if I glue
them on or if I just grout the spaces between each stone.
b) If I glue them on, I don't know how to keep the tops flat since each
stone is slightly different in thickness.
c) Even though the base starts at 18" wide, it narrows to 15" wide but I
would want the stone to stay the same width.

Any advice is always appreciated!