I'm wondering if you can do this with constraints. I haven't used constraints in AutoCAD much, but in Inventor, you can make it flexible with angular constraints.

Thank you for your reply, 57gmc.

In the future I will try to use constrains to make the connection between the paths that the tubes must follow.
I'll try to solve getting information between objects first. I know that it is also possible to do this using Xdata, but I also have doubts whether this will be good for the future of the project.

Whey not create a cogo point grid that drapes onto the DEM, then create a surface from that.

I think this will create a better surface.  But I would use ArcGIS to put points in center of each DEM pixel and elevate each point to the correct DEM elevation.  Then have Civil 3D do the triangulation from those points. 

This is a good conversation. Just throwing out another idea.
Since this came from a DEM file, and from a plotting side you want it to be fast loading, etc.
Whey not create a cogo point grid that drapes onto the DEM, then create a surface from that.

Another idea, would be to do the same, then maybe from the DEM (point surface), explode the line work.
Use that as a basic xref. Then data refence the original DEM in with a surface display set to No Display.

Just some thoughts.

Surely there are people with more experience than me to answer. What I am going to expose here may not be completely correct as it is based on my experience and I hope someone corrects what is wrong.
I just have an app that makes use of something similar that you're aiming for and I haven't touched it in a while.
As the subject is vast I think it is difficult to get solutions right away. At least in my case, I adjusted it little by little and it took a long time for it to work properly.
Have a look at Deep Clone, HardPointerId, SoftPointerId, DBDictionary.TreatElementsAsHard, ObjectOverrule.
When you copy a "FlexTube" (within the same file or between files) you want it to have the same properties as the original.
If you look closely at Kean's example he uses DxfCode.SoftPointerId. From what I saw you are using DxfCode.Text.
There are differences between the usage of HardPointerId and SoftPointerId.
For "FlexTube" modifications I would implement this in entirely separate code via ObjectOverrule.
There is a content called AU2010 - CP230-1V - AutoCAD® .NET - Practical Examples of Customizing AutoCAD Entity Behavior from Autodesk University 2010 written in VB .NET by Stephen Preston which I think can help because it has examples that you can practice, of course it involves time.

Someone should port Delaunator to lisp as it can keep track of the half edges

I had some stuff here https://www.theswamp.org/index.php?topic=58049.msg613573#msg613573
But it’s been a while, if you follow the link in that post, it explains how to iterate triangles in order

I would have no clue how to change the resolution of a point set, except maybe eliminate nearest neighbors that are not on the edge and under some tolerance

The routine has been ported to Python, JavaScript, C++, a master lisper should be able to port it