How to realize walkable vehicles in a network game?

Imagine a moving ship with several players on it.

I want some kind of parenting going on so that if the players are standing still, their locations relativ to the ship location are not changing at all and no network synchronisation is going on (none for the players, still for the ship). The players should still be able to walk around just as if they would be simulated in a separate physics world that is acting as if the ship around them is standing at (0,0,0) and having it’s own static geometry to resemble rooms, walls, doors and all the inside props. But from the outside the ship just having basic primitive collision to handle the interaction with the world without making it to complex and jittery.

I don’t know if this separate physics world is even necessary. Maybe it is cleaner without it and the parenting alone is enough. Maybe even fake it and having all the inside collision of the ship and the player bodies fixed in a hidden world area with no visuals at all and transferring the positions to a visual duplicate which is parented to the ship.

Is is possible to have multiple physics worlds? Should I try faking it? Or should I forget all of this and just move the complete ship with all it’s players and props in absolute world position?