I see no real reason to second-guess the conclusions of professional therapists who worked with the child for months -- especially based on evidence provided by the father.
The couple didn't just get divorced, the mother had their marriage annulled because he repeatedly lied to her about his past. He lied about his previous marriages, military service and discharge, income, career, education. E.g. He exaggerated the amount of time he was a Marine (months, not years as he claimed). He failed to tell her that he was discharged from the Army because he admitted to being homosexual. He claimed he had a PhD, when apparently he didn't finish college.
It also seems like he is putting his own agenda above his concerns for the child. The mother, for example, kept quiet to protect the family and the kids. The father turned this into a cause celebre for the Red Hat set, including false accusations about the child's care. As a result, the judge put a gag order on the father.
So, you'll have to excuse me if I take claims from his camp (and the anti-transgender right-wingers who leaped to his side) with a huge grain of salt.