In thinking about the interconnectedness of people, when making a request for inclusion of one’s family in a Lightworker Healing Protocol session, where do the dividing lines stop in terms of first-degree, second-degree, third-degree relatives, etc?

The line will stop where your intention stops. If this is not clarified, then the divine realm lacks instructions and cannot unilaterally keep going and include a wider and wider circle. If this is specified, the divine realm can do so, and this will have paid many, many dividends. It is up to you, the limitation is on the side of human with the imagination as well as the energetic reach, but you have found the key to overcoming having too large a group to support with one session. And so without that limitation, why should there be a limit on the number of target subjects that can be included? There is no upper boundary. It is all dependent on your imagination and the specific instructions you include in the Protocol wording and set as your intention during the session.