I have a stone walk from the front of my house to the driveway, which
has three steps. The stones that form the top step have come loose
and I want to reset them. These stones sit half on dirt and half on
other stones that serve as risers from the step below. I couldn't
tell if there was any gravel or sand used under the half on dirt. For
the other half, it looks as though something was used between the
riser stone and the step stone, but roots have grown in between and
compromised whatever was there.

Any suggestions as to how I should reset these stones?

Thanks!

-Ben