If the Dimonds are schismatic, then that also holds for Father Pfeiffer.
Fr. Pfeiffer is schismatic for 2 reasons.
1) Asking Catholics to shun other valid traditional Catholic priests and their sacraments.
2) Permitting a schismatic fraud to feign the Holy Sacrifice of the Mass, and continuing to boldly defend said schismatic fraud rather than being repentant for his folly.