In the base game you could glitch yourself up too 4 followers or three if you've (spoilers) killed Cicero at the end of the Dark Brotherhood quest line. (end spoilers.)
I've tried this after installing Dawnguard and it worked.
I've tried this after installing Dawnguard with Serana and it didn't work.
Why I wonder, because underneath certain YouTube videos I saw commands that you can.

I hope you guys know a way.