7 Kings are the 7 Popes, starting with Pius XI. The 10 horns are the Cardinals that take over the Church during the period of the Fourth and last beast of Daniel, starting with Bergoglio and his gang of Cardinal advisers.
It all started with Pius XI because he refused to Consecrate Russia to the Immaculate Heart. And the Lateran Treaty was the final collapse of the temporal power, making the Holy See unable to sustain itself without reliance on the secular powers controlled by Fɾҽҽmαsσɳɾყ.
You're right ... it was 7 Kings, with 10 horns and/or crowns. There was someone here posting about that Francis of Palau, and I think he likened the horns/crowns to 10 temporal leaders or something, not Cardinals. It's so hard to say, that it's little more than guess work.
What I do find striking, though, and hard to ignore is the likenss of the Whore of Babylon to the Conciliar Church, and that dovetails also with Francis of Palau's take on it.