What is or is not a "branch" is unimportant. If you have read the link you'll know that a "branch" is not a point mass but a blob spread out in configuration space. All MWI needs is "the probability density of finding oneself in point x in the wavefunction is the amplitude squared at that point". It's standard probability theory then to integrate over a "branch" to find your probability of being in that branch. But the only reason to care about "branches" is because the world looks precisely identical to an observer at every point in that branch.