Have not tried it but should be easy enough to test.
For anything to work you have to begin with the context of of how objects needs to interact as a series of events and lets say the player is already on the ship.
You can make the ship a character BP and give it it’s own animation BP. A good starting point would be to make use of the flying template which already has everything set up.
You will have to do some editing like making the ship a room that the player is contained with in.as to typical behavior of the player walking around it as an environment space. Collision and stuff.
You could then try making the character a component of the ship so that it inherits the movement of the ship and add it’s own animation BP to walk around it. This could even be another character BP containing it’s own movement component.
A bit more complex than it might need to be but the ship can be controlled independent from the player and if replication is needed it’s all handled for you via the movement component.
A simpler way would be to link the character to the ship (flying room) so that it becomes a child of the ship but it’s transform becomes relative to the location of the ship as the parent and not the world. Things like gravity can then be changed independently between the ship and character but the characters position will be constrained by it’s parent.
As I said I have not tested the theory but the problem I’m seeing is based on an assumption that both the ship and the character have to be relative to world space where the characters position needs to be relative to the ship which is child of world space.