miners will not allow double spends to happen.
Correct. A "true" double spend, where both transactions are confirmed in the blockchain is impossible.
in the most rare circumstance and it will probably happen a few times, if everything arrives at the exact same smallest unit of time measurement used in the btc protocol, it could happen.

What are you talking about? It is not possible for both transactions to be confirmed. It doesn't matter how close together they arrive.