I don’t believe that using level streaming is a feasible solution to this problem. This is something I have looked into and here are the components I believe you would need to get it to work.
First you need a custom gravity system so that your characters all have gravity pointing toward the floor of your spaceship (I am assuming this is what you are a looking for). There are a few free custom gravity plugins out there on the forums. I have tried a couple of them and they seems like they might work for this with a few minor modifications. Here is one that I tried. I think there are a few others too.
The second problem you will run into is the Character class. It stays Z aligned which is going to be problematic for a character standing on a spaceship that can spin on all three axis. I believe you would need to either create your own customer Character class or start with the existing Character class source code and rewrite quite a bit.
Then if it is a multiplayer space game you will eventually run into the WORLD_MAX issue.
So there are a lot of obstacles to building a multiplayer space game in UE4 where players can walk around a ship, but it would be awesome if someone gets it working. Best of luck!