First, 'brother' Dimond is a fraud. He pretends to have Holy Orders, which, if I am not mistaken, is a sacrilege. At the very least. he's rather childish to go around pretending to be in a 'monastery' that is purported to be his house.
Second, what a Brother or a 'brother' or whoever 'condemns' is irrelevant; he is not in any way responsible for defining faith and morals for the Church.
Third, sedevacantism (so-called) is an OPINION that one may choose to have or not. I, for one, believe that the See is currently vacant because of Ratzinger's rampant Modernist heresies. That goes TRIPLE for Wojtyla, who was about as UnCatholic as a person can get without publicly repudiating the Faith in so many words. JPI may or may not have been a valid Pope; I don't know enough about his life except that in his short reign he did nothing public to refute or reverse any of the damage caused by the Council.
Paul VI was an apostate who deliberately attempted to promulgate a New Order of 'mass', the existence of which is a slap in the face to Holy Church and to Pope St. Pius V.
John XXIII was a Freemason and a Modernist who thought the Church needed 'renewing'. Perhaps he would have been better served encouraging the Faith people were LEAVING, rather than attempting to reinvent the wheel.
In short, what Dimond thinks is immaterial. He and his brother are impostors and therefore have nothing to add to the discussion re: the validity of a Pope.
Pope St. Pius V, pray for us.
Immaculate Heart of Mary, triumph soon.
Sacred Heart of Jesus, have mercy on us.