Since they separate themselves from the majority of Catholics -- the Mystical Body of Christ -- does that not make them schismatic?
I believe it does.
They are to be avoided. Despite a good video against evolution, and maybe a couple other decent videos (even a blind squirrel finds a nut once in a while), you're not going to lose much by steering completely clear of this dangerous group.
Ending up a home aloner is NOT a recipe for salvation.
From the attached:
1. They call themselves “Brothers”, but neither of them has made the standard novitiate, which the Code says is strictly necessary for professed religious. They call themselves “Brothers” because this lends prestige to their opinions....
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13. The two “Brothers” Dimond are two worrisome little men. Without any authorization and without proper theological training, they have endeavored to establish themselves as teachers of the faithful and ‘certifiers’ of all priests in this country. They make a lot of money with their misleading publications, tapes, etc., and they spend much time on the phone persuading people to stay away from the Masses of non-Sedevacantist priests. Who knows how many Catholics of good will have been persuaded to stay home for months on end -- even years -- rather than attend Mass, confess their sins, and receive Holy Communion? I urge everyone to give these men a wide berth; do not buy or circulate their materials, even those which are acceptable. Do not send them money. Beware of wolves in monk’s habits.