Sort surface curves into three separate list

I am trying to separate the curves from this mass into three separate list as like

  1. diagonal left
  2. diagonal right
  3. the perimeter curves
    But do not have an idea about how to proceed further. Once I try to isolate the perimeter curve using Surface,Perimeter curve node I am getting the curve from the location of mass in the family environment. not from the location of mass in the project environment as you can see in the attached pic.
    I hope somebody can guide me in the correct way to solve this problem.

    I am attaching my graph here for your review.
    Beam By curve - V2.1.dyn (23.7 KB)