If you are using the Garmin coupler you need to cross both. As it is Intended to connect 2 Crossed Garmin cables
and will cross a 3rd time inside the coupler. So you end up with 1 cross total.
If you are using a non Garmin normal rj45 coupler. Then only 1 cable can be crossed and 1 not.
cables must be crossed.
You must use the Garmin hub as it has poe functions to wake up all the devices.