You should provide a copy of your project for investigations as what you are currently asking for is a crystal ball prediction.
For the top left tank on the peer screen, possibly are you having a tank instance in your layout by default that does not get destroyed on start of layout on the peer side.
If that object has the "bound to layout" behavior, that is a common thing that may happen.
For the light cast, hard to say without the hands on the project.
Also, the casting behavior is possibly not designed to be used over multiplayer to be used as fog of war.
You'll possibly have to make a render on your host, and then pass it on to the peers so they display it in the same vein through multiplayer messages.