Just in case anybody is doubting anything that Julie is saying here I dug out one of my old genetics manuals and here is a blurb:
XXY - This condition is called Klinefelter syndrom. Affected persons are male. They tend to be tall, do NOT undergo normal sexual maturation, are STERILE, and in some cases have enlargement of the breasts. Mild mental impairment is common.
See, this is a genetic thing because the affected person has an extra chromosome, the result of a non-disjunction failure during meiosis and have it their whole lives. It can't be turned on at any time. My reproductive physiology book says that "individuals have small external genitalia, crptorchid testes, and are mentally retarded."
As I see it Chloe doesn't exhibit any of these symptoms and it can be easily proven because Chloe obviously wasn't sterile and fathered 2 beautiful children who are both obviously normal.
Now, upon further research I find that it not only is theoretically possible for XXY males to father children, obviously they would only be able to father boys, but that the major impediment is low sperm counts which can be treated to some extent. Also, the vast majority of XXY males never develop the syndrome. They are normal except for being slightly behind in language areas. So now I am changing my mind a bit. It is not likely but may be possible as both kids are boys. If one would have been a girl then it would have been 100% impossible.