Infallibility is meaningless for sedevacantists. They say they follow the Church but whenever they find something they disagree with coming from a Churchman (even the Pope) they do not change their opinion, they just declare the Churchman to be a heretic who lost his office based on their own private judgment. In practice they are all their own Popes.
Similarly, the teaching Church is also meaningless to SSPX supporters, because they say the Church is not always infallible and they sort the teachings of the Churchmen and accept those they like while rejecting those they do not like, also based on their own private judgment. So in practice they are also all their own Popes.
I do not know what position is Catholic.