Heh, welcome to the club, Jonathan. My family keeps denying that I can be really trans because they claim they "didn't see it" in me when I was growing up. They didn't see how miserably I failed to fit into male situations? How I preferred the company of girls? Part of it is that they have been covering their eyes to prevent themselves from seeing what they don't want to see. Part of it is that I was intimidated into going along with their system. I even hid the truth from myself because it was too hard to deal with. Yeah, I colluded in their denial--and now that I've blown the lid off, they're angry at me for telling my truth now. If I'd come out with it when young, they would have had the same reaction anyway. I always knew within me that I could not fit into the male gender, but did not dare to openly question it. The enforcement is too pervasive and too violent against those who step out of line, and I was not that bold. As a result, I isolated myself a lot, because male society was repulsive to me, and I wasn't allowed into female society.
I think it's those with assertive personalities who are the source of the stereotype that all trans people have to proclaim it from a soapbox in no uncertain terms beginning from the age of 3. But I'm not the assertive type. I always shrank from confrontation and hid away. It took me until the age of 45 before I grew enough of a backbone to come out of hiding and stand up for my truth. Instead of welcoming the honesty and strength of character this took, they try to shoot me down.
I also think my Mom holds a stereotype that all trans women have to come from a gay background, and since I dated girls, she takes that as "proof" that I can't be trans. Just like in Blanchard and Bailey's theories, although I doubt Mom has ever heard of them, Blanchard and Bailey are just playing off of certain old stereotypes that have nothing to do with actual gender identity. Actually, early on I had been sexually attracted to boys, but after two of them raped me, I got turned off of liking males.
This sort of denial can be so hardened and entrenched, it becomes unassailable. I wrote out for my Mom a detailed history of 40 examples of my cross-gender behavior as I grew up, going back to the age of 4. Right from the beginning of my preschool, the first gendered environment I was ever placed into, I rejected identification with the boys and placed myself with the girls, a pattern that persisted thereafter no matter how hard my family and schools tried to suppress it. I wrote out some deeply revealing private facts about my gender and sexual history which I'd never told anyone. Mom accused me of making it all up based on what I'd read about transsexualism. She basically called me a liar after I'd taken her into my confidence and revealed my most private secrets--that hurt me worse than anything else ever has.
So be prepared for family denial that will go to any lengths of stubbornness to keep the truth at bay. And never mind it. You know your truth and it will set you free.