Also, anyone can confirm that sgtbx is tightly embedded is cctbx and cannot be used standalone?

sgtbx can be used as a pure C++ library and as such it depends only on a few parts of cctbx (Miller indices, unit cell, and a few miscellaneous utilities: i.e. a very small fraction of the whole cctbx module), and on a few parts of scitbx (arrays, integer matrix row echelon reduction), and hashes from the Boost library. As a Python library, the dependencies are more numerous.

If you could tell us what is your ultimate goal, we could provide more help.