Mith-
Perhaps this is the sticking poiont for you:
You seem to be focusing on the numbers (i.e., the bishops dispersed in union with the pope).
Rather, it is the CONTENT of what they are teaching which should hold your attention.
If the content is not contained or compatible with the ordinary infallible magisterium (whether it be a pope, or the pope and all the bishops, or just a bishop), then it can only represent the authentic magisterium.
Otherwise, you would be saying that teachings incompatible with the faith must be believed.
In other words, your solution to this fact is to deny these men hold any office in the Church.
My solution is simply to recognize the threefold magisterial distinction, and that these novel teachings of the authentic magisterium carry no weight.
Herein lies the heart of the conflict between sedes and R&R.