Tegmark IV and many worlds have little to nothing to do with each other.

• The Everett branches of the "many worlds" all follow the same physical laws -- the same equations.
• Tegmark IV demands that every possible alternate set of equations is equally "real" as our own, that a concept existing in abstract mathematical form and a physical structure existing in reality is one and the same thing. Effectively it attempts to explain reality by arguing the word reality has no meaning.