Boundary surfaces with holes - Data management

Hey People,

I want to create boundary surfaces with holes but I have a data management problem.

The existing posts I found couldn't help me.

I want the rectangle inside to have a certain distance from two outer sides so I measured the distance and created tween curves. I combined two points on each to a polyline and cut that out.

So that worked for one surface, but when I enter more than one, it messes up and I don't know how to keep them seperately.

Could anyone help me with this?

Best,

Valentin