Instancing in Garry's Mod and how to load other instances

So I’ve been thinking for awhile now and haven’t actually though of a bullet proof way of how to do this. What I plan on doing is instancing however I always run into the problem illustrated below.

Say we have two players, player A and player B. Now lets say player A is in an instance of the map like this where A is the player and = are the other instances

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==A==

All is well for player A, but now here is where I run into the problem. Let’s say player A is on the edge of his instance about to cross into the next one, and player B is in the instance he is about to cross into like this.

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==AB=

What would be the best way to have the instances compare to draw player A to player B and player B to player A? Also imagine it as a 3d cube instead of a 2d square.