Creating and Offsetting Polylines From Multiple Surfaces

Hello guys!

I have a bunch of triangular surfaces and from each one of them I want to extract a boundary curve, offset it and use that offset to split the surface. I am able to do that for a singular surface, but it gets messy when I try to choose multiple surfaces.

As you see here, the offset lines move inward for some surfaces and outward for for the others. How can that be addressed?

Here are all the surfaces(299) that I need to have their boundary lines offset:

Help would be highly appreciated