Modding Help How Does Multiplayer Work, Exactly?

I know this doesn't sound like a modding issue, but it does involve modding, just in case somebody decides to point that out. I've been trying to secretly work on a multiplayer-oriented mission, but I have too many questions to keep its existence unknown. I won't reveal anything else about it, however, unless its absolutely necessary.

My questions are as follows:

• How do radio messages work? Are they global or local? In other words, if one player receives a radio message, will everyone else also receive it?
• Will loot dropped by enemies be visible to everyone, or only the player who dealt the final blow?
• Is it even possible for multiple players to be in the same instance world with each other? or will they all be sent to separate instances?