How do I add a series of timeline topics to a boundary?

Since timeline and flowchart topics is children of children of children, sometime only one child pr generation, how do I add several of these into a boundary.
I'm trying to use flow chart and timelines to describe initialization processes and program initial startup and add these to two boundaries, one for the process of unit initializations and a boundary for the flow inside program main unt initialization.

Seems like a get only just add boundaries around each subtopic and has to redo everything instead of just being able to import the already made flowchart which I now want to redesign.