Please note: this has nothing to do with authority or jurisdiction.
What +Williamson said is that he has no authority to bind all the Resistant priests to obey him. And that was completely true, and still is true.
+Faure is merely "giving it a go". He's starting a society, and at the very least he will incardinate those who he forms at his seminary after they are ordained. It's not that he doesn't have the right to start a congregation.
Archbishop Lefebvre started a society, and many followed him because of his charisma, his reputation, his holiness, and most of all his stellar career which reached so high it even touched the papacy (he was appointed by the pope to be the Papal Legate to French Speaking Africa).
Long story short, +Lefebvre's resume was far more impressive than even +Williamson's -- and +Williamson would be the first to admit this. (He is humble enough that he would never suggest, let alone claim, otherwise.)
It has to do with authority, which always comes from above. If a good Resistant priest didn't want to join +Faure's new group, he wouldn't have to. It might be prudent for him to do so, but it wouldn't be a sin or even a fault if he wanted to pass on joining.
Long story short, it's not as simple as a bishop jumping up on the table like a gorilla and grunting, "Me Bishop. You Priest. You follow!"
That would imply that there is an inherent authority or jurisdiction contained in the office of Bishop itself. But that's not true. There is power of Orders, and power of jurisdiction. The 4 +Lefebvre bishops, for example, have valid orders but they were never given any jurisdiction (authority). If +Lefebvre had attempted the latter, it would have been a schismatic act and he would have been ipso facto excommunicated (which is what all the Conciliarists think happened).