What are these interfaces?
That is expected so far. It's just cosmetic, you don't have to take care about interfaces at the guest level.
These are the internal interfaces the guest is using, they're mostly just there for stats purposes, you don't need to do anything with them.
They also show in the hypervisor via tmsh show net interface -hidden.
For more information about interface assignment, refer to K03740927: Understanding interface assignment for vCMP guests.