There is an election process, and all core python team members vote on the SC (https://peps.python.org/pep-8105/#results) for a 1-year term.

Greg, Thomas, and Barry are all old guard (20+ years as core devs), Emily and Pablo are relatively more recent, but still have 5+ years as core devs and are I believe more actively doing python feature development. All of these folks have served on the steering council before, some for 3-4 years.

Guido has served on the SC before, but has been stepping back recently.