Traffic Inspector + PPPoE how to set up?

Question

Network administration

On the server is Traffic Inspector. From it the Internet from two providers is distributed.
1: Rostelecom (PPPoE) STK Internet interface name
2: SCS (WAN) CKC Internet interface name
The "Administration" user group has a route to STK Internet (or rather, its PPPoE created in routing and remote access)
The "Teachers" user group has a route route to CKC Internet
Now the system works like this:
If the CKC Internet interface falls off, then users are redirected to the additional STK Internet interface, which is not required!!!!
That is, if a group is assigned a route to CKC Internet, then when this interface falls off, the group should not be redirected to STK Internet. The group should just be left with no internet at all!
I so understand it is necessary for this group to forbid to go through STK Internet in rules of users. But I tried to disable the route on STK Internet. Nothing happened.
How to correctly create a filter for two interfaces so that they serve only those groups to which they are assigned?
There is a kind of FAQ on this topic for TI, but it is as old as mammoth tusks and is not at all understandable for new versions of TI.
I think I explained clearly.
And just the same question about just the same PPPoE. I was told that Advanced Routing does not work with virtual interfaces, which means that it will not work with PPPoE.
But nevertheless, I have assigned the PPPoE interface to the user group, and the CKC Internet interface to another WAN. Everything seems to be working. Some go over PPPoE others over WAN.
If Advanced Routing does not work with PPPoE interfaces, then how can I properly configure the route? If I specify the STC Internet interface through which PPPoE is connected, it does not work that way.