I'm sorry to hear about your situation. You need to retain an immigration attorney to consult with you about the VAWA requirements. If you cannot afford an attorney, contact your local bar association for a referral to a non profit group or pro bono attorney in your area.
Transgender cases are complex, and the USCIS rules, guidelines and interpretations of the immigration law have not been stable and consistent in the past years. You should consult an immigration attorney about your situation and other options your fiance may have for returning to the U.S.
His daughter can sponsor him when she turns 21 and has the financial ability to support him (or has a co-sponsor with sufficient income). If he would like to be a permanent resident sooner, he will need to pursue other immigration options such as a temporary work visa. He should schedule a consultation with an immigration attorney to discuss his options.
It is not possible to speak directly to a USCIS adjudicator. This is why we encourage you to file your case through an experienced immigration attorney so that it is prepared properly, without any additional explanations being necessary.
USCIS does not consider omitting a marriage from your immigration application documents "benign." I strongly suggest you not discuss this on an open forum like Avvo and consult with an immigration attorney in confidence at once.