You need to navmesh the interior, and don't forget to finalize both navmeshes, the interior and the exterior cell containing the exterior door, once you finalize the navmesh you'll see a yellow triangle under the door markers, once you have proper navmesh outside and inside your companions will follow you like any other interior. ~~I have the yellow door/teleport maker under the navmesh same I as I would for FNV. It won't turn yellow. I see what youre talking about in other cells but idk what im not doing.~~ I figured out how do what you mentioned.