Given that the devices connect to the same Access Point, obviously share the same password, and are in range to pick up each other's radio, could malicious software on one of my laptops, given sufficient low-level access to the WiFi hardware, decrypt the traffic from my other laptop?
Let me tackle the first part of the question with the basics. Each node in the network has it's own encryption key with the access point. This makes it not possible to simply decrypt everyone's traffic just by sharing the network.
But, is it possible to get the other node's traffic? Yes. There are a variety of ways. For instance, I could mimic the AP and force the other nodes to connect through my laptop. Then I see everyone's traffic in the clear.
I'm making some assumptions as to what your core question is, though.