You're welcome Ankhesenamun. i see your point about Tiy and Kiya and i agree with you.
So is Nefertiti, Ay's daughter? Another million dollar question. Again the answer is there is no solid proof. So why do some and by all means not all experts believe Ay is Nefertiti's father. In part because of the titles Ay shares in common with Yuya... the reason this time is, well Yuya was the father-in-law of Amenhotep III therefore Ay must be the father of Nefertiti because he has the same powerful titles i.e., father of the God, and Master of the Horse. However how being father of the God relates to being the father of the Pharaohs' wife isn't explained. Anymore than being Master of the Horse relates to being the father of Pharaohs' wife.
Another often quoted "proof" is that in the early Amarna reliefs that survive we can find Mutnodjmet, whose only title is 'sister of Nefertiti'. We do know that in Ay's tomb at Amarna, Mutnodjmet is despicted in it. This being taken as 'proof' that she was his daughter. However, Nefertiti is not recongized in it other than as his Queen at the side of Akhenaten.
Here the discussion usually turns to the only known wife of Ay. Often called Tiy II, to keep her seperate from Queen Tiy and because in Ay's royal tomb she is recongized as his own Great Royal wife. Although it is generally accepted that she was dead long before he came to the throne. Tiy II, in surviving Amarna reliefs has only the title as the Goddess' Nurse and Governess. She is never recongized as Nefertiti's mother, therefore she is not accepted as being the mother of Nefertiti. i am not even sure if she is universially accepted as the mother of Mutnodjmet. i have read some experts that accept the theory that Ay was the brother of Q. Tiy I, was actually raising his nieces the daughters, of yet another unknown sibbling of Q. Tiy I. Yet, if this theory holds any water, they do not explain why Mutnodjmet is in Ay's tomb as a daughter while Nefertiti is not. Other experts explain that Nefertiti is actually Ay's daughter by some unknown first wife. Again if this is true why is neither of them in his tomb?
So we have only a few surviving reliefs where Ay's daughter Mutnodjmet is called the 'sister of Nefertiti'. We can accept this literally as most do. Or we can ask IS THERE ANY OTHER POSSIBLE EXPLAINATION FOR THIS? Again, yes there is and it is in Tiy II being the recongized "the nurse" of Nefertiti. Throughtout, history the children of nurses are often considered as a kind of sibling to the nursing child belonging to another couple. Since Mutnodjmet, was the child of Ay, a very important offical of Akhenaten, and the child(?) of Tiy II the Nurse and Governess of Nefertiti. Mutnodjmet's title of being "sister" to Nefertiti might have been strictly honorific and not biological at all.
The third "proof" accepted of Ay being Nefertiti's father by those that accept it. Is that Horemheb did marry a woman with the name of Mutnodjmet. In one of his reliefs, he claims that the "daughter of Pharaoh bowed to him".
Since most experts kill, Q. Ankhesenamun, off shortly after a forced marriage to Ay, to cement his right to the throne. And all of her sisters at about the same time as Tutankhamun succeeds to the throne. This leaves very few "daughter(s) of Pharaoh" around to be bowing to Horemheb.
These experts reason it had to be Mutnodjmet the daughter of Pharaoh Ay. Of course these experts claim this gives Horemheb the 'right' to the throne. Because he married the daughter of Pharaoh. Of course Amenhotep III and Akhenaten didn't do this and it did not seem to threaten their rights to the throne is dismissed. The fact is... the Mutnodjmet that Horemheb did marry is not claimed by him or her to be the daughter of Pharaoh Ay and as one expert stated may not even be the same person.
So there you have it... is Ay's Nefertiti father? Since none of the "proofs" are really anything substantial, i don't accept Ay as Nefertiti's father. Of course you and others are free to accept the proofs as given.
As for Tiy being a nickname of Nefertiti. i do believe i have read something along that line myself. Nothing current i assure you... today, it is too well known that they were two different women. Or three if you count Ay's wifely Tiy.
Venturing a guess i would suggest that it relates to Dr. Velikovsky's work titled Akhenaten and Oedipus. In this book, he compares the known life at his time (1930-1956) of AKhenaten with the character from a play by a Greek writer some 900 years after the death and forgotten memory of AKhenaten. It is an interesting theory where he believes that Akhenaten (Oedipus) married his mother Queen Tiy. Here may be the source of the Tiy is a nickname for Nefertiti, it may not too but it is the only thing i can think of that might account for it.
i hope this is a help
and have a nice day.
If you are interested in more of this Akhenaten/Oedipus work of Dr. Velikovsky. Please go the Pharaohs topic and cursor down until you find the thread Akhenaten/Oedipus the theory is explored in some depht there.