In searching through some of my books I did find some info.
His titles under Akhenaten were "fanbearer on the right of the king," "over seer of all the horses of the lord of the Two Lands," "true royal scribe," " chief of archers", and the most important "God's Father": a title that his presumed father ,Yuya, held under Amenhotep III. He may not have been a priest, but perhaps a military man.
In Cyril Aldrid's "Akhenaten:King of Egypt" he writes:
"It is extremely unlikely that this important family [the family of Yuya and Tuya], so closely connected with royalty for several generations at least , did not have another son to carry on the tradition of arms that they professed, since Anen had evidently deserted a military calling for sacerdotal office. We do not have to look far for such a succesor. In the next generation at the court of Akhenaten, we find a Divisional Commander, Ay, holding most of the titles and offices claimed by Yuya under Amenhotep III. Both refered to themselves as 'One Trusted by the Goood God [the king] in the Entire Land';as 'Foremost among the Companions of the King'; and as 'Praised of the Good God'. These titles are generally taken to be honorific: on the other hand they may convey some degree of kinship with the ruler. Ay was a 'Fan-bearer on the Right of the King', and 'King's Own Scribe', or personall secretary (Aldred 220)."
"There is also another connection between these men. Yuya held important offices in Akhmim near where his daughter Tiye had extensive estates. Ay also built a chapel there to its local god Min, presumably because it was his birth place or family seat. It is noteworthy that references to Min and names compounded with Min and the goddess Mut became common in court circles at the time of the ascendancy of this family."(Aldred 221)"
"The title that Ay uses in preference to any others is 'Father of the God', which he even incorporated into his nomen when he became king on the death of Tutankhamun. The title usually denotes the holder of a priestly office and historians in the past have refered to Ay as the 'Priest Ay', accrediting him with some of the religious thinking behind the Aten heresy, largely because the much quoted Great Hymn to the Aten appears in it's fullest form in his tomb at Amarna. But Ay was primarily a soldier and held no priestly offices at Amarna where Pinhasy, Pentu and Tutu officiated as Chief Servitors, and Meryre I as High Priest. Moreover Ay is the only dignitary at Amarna to bear the title of 'Father of the God'. Many years ago the German scholar Ludwig Borchardt argued that in some circumstances this ambiguous title could mean 'The Father-in-law of the Pharaoh', and this is particulary the case with Yuya, who is stated on two of the commemorative scarabs of Amenhotep III to be the father of Tiye, the distinction, 'Father of the God', where there was no space for other titles. It would appear, therefore, that Ay too must have been the father-in-law of a king, though Akehenaten was the monarch he served. In that case, Ay's daughter must have been a wife of the pharaoh, and presumably his chief wife. Such a person can only have been Nefertiti (Aldred 221)."
Nicholas Reeves contradicts Aldrids (Borchardt) attempt at explaining the title of "God's Father" as meaning Father-in-law in a paragraph on pg 58 of his book "Egypt's False Prophet: Akhenaten" by stating Ay's brother held this tilte prior to Ay. He also gives another reference to Ay's military career:
"Most important of all, howevever, was the man assumed to be the third off-spring of Yuya and Tjuyu, the military officer Ay. He, like Aanen, would inherit Yuya's principle title 'God's Father', and - as events would show - every ounce of his political influence as well (Reeves 58 )."
Reeves further questions Ay's relationship to not only Akhenaten but Nefertiti herself:
"In fact on present evidence, the probability is that Nefertiti was Egyptian born and bred. Her nurse was none other than Tiy - to be distinguished by the spelling from Amenhotep III's principal consort - who was the wife of Ay, likely brother-in-law to the old king Amenhotep III and uncle of Amenhotep IV. Might Ay have been Nefertiti's father? On analogy with the status of Ay's supposed father, Yuya, it is conceivable that Ay too wished his title 'God's Father' to be construed literally as father-in-law to the king; it was certainly a label by which he himself set agreat store, since it would later be incorporated in his kingly nomen, almost in support of his claim to the throne. But, if Ay was Nefertiti's father, why is Tiy identified merely as'nurse'? Perhaps she was simply a later wife of Ay, rather than Nefertiti's actual mother.
Certainly if Ay did father Nefertiti, he would have been continuing in the the tradition of marrying into the royal household upon which his family's fortunes seem at least in part to have been based. The high favour he enjoyed as a mere officer of the new regime would also be explained, as also his subsequent allocation of a large and impressive tomb at el-Amarna - to say nothing of his future elevation to the kingship itlself. The further implication would be that Mutbenrte/Mutnedjmet was anothe offspring, with both daughters (half-)sister to Ay's supposed son, Nakhtmin - whom Ay, as pharaoh, would later invest heavily in his hopes for the future (Reeves 89)."
This is all I have found so far but I will continue to search through my library.