(13) why John the Baptist

This is a connection that will make sense once the Nahuatl chronology is explained. In the Nahuatl chronology, the Eden scene (part of or perhaps the whole left panel of the triptych) corresponds to the 1524 arrival of Franciscan missionaries in New Spain, where they baptized people in great numbers. Isabel Mateo Gomez's complicated explanation of how if the man in the cave is John the Baptist, the woman is Eve and the person in the back of the cave might be Adam, is easier to understand once the Eden scene is read as an allegory of baptism. (In other words, Carlos I and Juana I were co-regents of Spain, and the Spanish were in New Spain for the purpose of baptizing people.) Juana is still more impressive than her son the emperor since she is like Eve, the ancestor of everyone.
There is also some irony, since the inhabitants of the New World were likely to be more skeptical than Adam and Eve were on the sixth day of Creation when they were only a few hours old. It is not clear to what extent the group in the cave relates to New World histories involving caves and mothers of twins (Juana actually had six children including two sons).