That is a sedevacantist organization.
Sedevacantism is a non-starter. Since there are no cardinals left from the time of Pius XII’s death, who do they suppose would elect a new pope? There would be no way, thus making a liar out of God and his promise to remain with the church until the end of time.
“...Since there are no cardinals left from the time of Pius XII’s death, who do they suppose would elect a new pope? There would be no way. ...”
Can you quote official Church teaching to this effect or is this your own interpretation?