Sharing membership across multiple instances

To have separate domains for a newsletter and podcast, both powered by Ghost and ideally sharing the same membership, it seems like the options might be:

  1. two instances of Ghost with memberships synchronized via Zapier.
  2. one headless instance of Ghost with all the content organized into collections, and two instances that are just front-ends.

It seems like most posts talk about using a static-site generator for the front-end: is it even possible to use Ghost as a front-end? Have I missed any other options?