In Everflow we use sub2 to pass clickid, but RedTrack has sub2 used for another parameter

Everflow subs are not connected with our subs that way. These are two different lines of parameters: traffic channel → RedTrack and RedTarck → Everflow.
Everflow has subs to record what you want to send them.
What does it mean? First we record values from Facebook (or any other channel), and then can send it to Everflow if needed.
The link on FB can be

The Everflow link (offer link in RedTrack) then is:

Where the first sub2 is the Everflow param to catch our clickid.
The second {sub2} is your keyword received from FB before and it can also be sent to Everflow.

Here and here is more info on the matter