Incorrect as regards to Catholics. Catholics do not believe Mary remained a virgin all her life. Correct that Catholics, unlike Protestants, don't believe Jesus had younger siblings. The author of the article doesn't really understand Christian dogma, regardless of denomination.
Incorrect. The belief in the perpetual virginity of the Blessed Virgin Mary is a tenet of Catholicism and was also shared by Calvin, Luther and Zwingli.
The belief that the Blessed Virgin Mary was not a perpetual virgin is a relatively novel one amongst protestants.
Sorry, not so. The dogma of the Perpetual Virginity was promulgated by the Council of Chalcedon in 451 AD, and so is binding on all Roman Catholics.