I've given my custom followers the playerfollower package, set their relationship rank to 3, and done a setplayerteammate() on them, but they will only follow me inside of the cell they are created in. I've checked the Navmesh, and the green triangles are where they should be...I'm confused.

I assume you have the potentialfollowerfaction, currentfollowerfaction -1, and relationship set up (requires NPC to be unique for the relationship) correctly?

They aren't real followers to be honest, just dwemer automatons you can create that follow you around and help in combat. So, I didn't put them in the faction or set up a relationship. I don't think those steps are necessary to what I'm trying to accomplish though.