This was checked by my friend Stephan Borgehammar, author of How the Holy Cross Was Found, I am, with his permission, reprinting what he found out:
The "horrible findings" seem to be partly errors of fact, partly misunderstandings.
The article of the Inquisition from 1647 is not quoted, so it can't be assessed.
The papal statements from 1331 and 1920 cannot be identified on basis of the information given (Clemens VI was not yet pope in 1331 so in that particular case either the year or the name of the pope is wrong).
The papal statements of 1327 and 1907 would seem to be the following:
Medieval Sourcebook (internet resource): The following sentences taken from Marsilius of Padua and John of Jandun were condemned by John XXII, 1327[...]
(2) That St. Peter had no more authority than the other apostles, and was not the head over the other apostles; and that Christ left behind no head of the church, and did not appoint anyone as his vicar. (Latin original, quoted from Denzinger Enchiridion no. 942: "Quod beatus Petrus Apostolus non plus auctoritatis habuit quam alii Apostoli habuerunt [non fuit plus caput Ecclesiae quam quilibet aliorum Apostolorum], nec aliorum apostolorum fuit caput. Item quod Christus nullum caput dimisit Ecclesiae, nec aliquem suum vicarium fecit."  = variant reading from the concluding section of the bull.)
Pius X, 1907, Decr. "Lamentabili" - list of teachings of the modernists that the pope condemned:
55. Simon Peter never even supposed that Christ required him to exercize primacy in the church. (My* translation from Denzinger no. 3455: "Simon Petrus ne suspicatus quidem umquam est, sibi a Christo demandatum esse primatum in ecclesia.")
There is a good, simple exposition by Jeff Ziegler of Catholic doctrine on the subordination of Paul here:
No honest Christian can object to what is said by Ziegler here.
Here ends the quote from Borgehammar.
*My=Stephan Borgehammars, not mine.