Massey's Horus claims can be checked directly against the Egyptian sources he read, and every specific point fails the check. Horus's conception is not a virgin birth. Plutarch's account, matching the Egyptian material, has Isis conceive Horus after using her own magic to revive her husband Osiris's body, murdered and dismembered by Set, long enough to conceive a child; this is a resurrection story attached to a conception, not virginal conception, and no Egyptian source uses language equivalent to the Gospel of Luke's account of Mary.
Horus has no twelve named followers anywhere in the Egyptian textual record. His myth names Isis, Thoth, Set and the tribunal of gods who judge his claim to the throne, a succession dispute settled by divine arbitration, not a teaching ministry with a following. And Horus is never crucified. His trial with Set is fought in contests of strength and legal argument before the divine court, ending in Horus's vindication and coronation as king, the model every living pharaoh then claimed for himself; there is no death scene to rise from.
Bart Ehrman's Did Jesus Exist? (2012) reviews the wider category of these parallel claims, including Massey's Horus material as it survives in later popularizations, and finds no ancient source supporting the specific list. The claim is not a live scholarly debate; it is a checkable point that does not survive contact with the texts Massey himself was reading.