I have a hAP AC. I have three computers and few wireless devices. Can anyone tell me how do I fast track local bandwidth, so that all my local devices communicate with each other at full bandwidth?

These devices are in same subnet? Then it's not fasttrack. Just put them in same bridge, which is probably already the case.
There should be a bridge with wlan & local ports, in it.

Edit: typo

Yes they are all in the same subnet and a bridge.

make sure you're bridge is hardware offloaded: that needs to be enabled, and depending on setup will be applied by ROS.

Yes, it is enabled in all ether ports except the ether1 which is the internet connection.

Then you're done!

Thank You.