[Silveras]

Containment is generally intended for fairly-permanent assignment.. geographic things like River A is on Continent B. Transitory things like memberships are recommended to be represented via Relationships (such as "Contains" type for "Organization/Member" pairs or "Residence/Resident" pairs).

So in your example... I would not use Cast Lists for the membership of the military organization or the ship's crew. The cast list might be "Adventure 1 NPCs". The "Band of Brothers" would be a "Group: Military" with each NPC having an "Organization/Member" relationship to it. Likewise, the "Ship of Fools" would be "Ship of Fools Crew" topic of the "Group: Other" type (unless something more specific fit), and again, the relevant Individuals would have an "Organization/Member" relationship to it.

Naturally, recommended practices are just that: recommended, not required.

The virtue to relationships is that there is a specific view that can be used to show the connections by type.

For my own uses, I place Individuals under Cast Lists for the most part, but significant NPCs are located where the PCs can most expect to meet them.. often in their adventure site "rooms".