"Whichever is earlier" refers to either: (1) "the kids wake me", or (2) "she (the sister) comes in (poured from the back of some taxi)" {i.e. arrives home drunk (Intoxicated) and/or hungover in a taxi}. The author will wake up at whichever of the two events above occurs first.

I have a brother.))))))

I think I've met your sister. ))))))