I think the issue you're having is communicating why you think multiplayer makes a significant difference here. It shouldn't. We're talking (basically) about a system where you chunk up the world and give each chunk its own local coordinate system. Everything in those chunks, including players, is tracked by a reference to its chunk ID and a local position within that chunk. It works just as well with one bullet in a chunk as it does a hundred bullets in a chunk, and it similarly works as well with one player as with a hundred players.
Where specifically do you see this falling apart with more than one player? Is it in this scenario below?
now without changing precision how would you keep one block away from the other without losing it's positional data (float would become in comprehensible after a limit)
What do you mean by "keep one block away from the other without losing its positional data?" They're separate chunks of the world with separate sets of objects (including potentially players) and don't need to interact until a chunk detects that an object is leaving its boundaries. At that point it figured out what chunk the object is going into and hands the object's current state over to that chunk. (As one possible example of how to handle the problem.)