The Sedevacantists have some powerful arguments. We should not read their material or listen to their arguments because they will beguile us unless we are extremely mature in our Catholic faith or are being supervised by someone who is. As a new Catholic I read their material and my foot nearly slipped. By the grace of God I was rescued and did not fall into their traps.
Of course everybody believes they are mature and settled in their faith, so I also urge that we take a very conservative view and assume that we are not mature enough to read their material.
If the Index of Prohibited Works was still in existence I have no doubt that this sedevacantist material would be on it. But of course me writing this is like putting a sign on a cupboard door that says “Do not look inside this cupboard”. That almost guarantees people to look into the cupboard because of curiosity. But curiosity killed the cat. Curiosity in matters of faith however kills sheep. So I urge everybody including the OP to avoid this issue for the sake of your eternal soul. Do not look at the Youtube video or persist in the debate. Truth does not come via clever debating skills. Truth comes from a quiet faith and trust in the church and her ageless teachings and her indefectable guidance.
Also we should not mock the Sedevacantists. Its not a laughing matter. Gerry Matatics was a wonderful convert from Protestantism and a wonderful defender of Catholic tradition. But he has been seduced by this powerful intellectual argument of the sedevacantists. As touching the power of reason and intellect you will not find anyone more skilled than Gerry Matatics, however what he lacks is childlike faith and trust in the church. His loss from Holy Mother Church is a terrible tragedy. We should all grieve for the loss of a favoured son, not mock and laugh. The arguments of the Sedevacantists are not childish, silly or ridiculous. If they were Gerry Matatics would not have been swayed by them. If Gerry Matatics can be turned from the true Church then this should be a warning to us all to stay away from Sedevacantism.