My younger brother is Trans, he and I were often mistaken for twins growing up. My older sister is Bi. My mom is a Lesbian, and my Uncle on my Dad's side is gay.
I wonder sometimes if, in a more accepting environment, there may be more queer people in my family. I think living in the closet is an accepted reality for many people, and I think it is more true for people of older generations. My mom, in particular, I think could actually be trans, if she were open to the idea. But she's pretty set in her ways, and being a Mom is a huge part of her identity...
Regarding the environmental factors, well, I think both my parents did their fair share of drugs in the 60s/70s, my Dad most especially. I've noticed there's a tendency for him to more or less believe that Psychedelics could be responsible for just about anything. He's even mentioned he thinks they changed him 'genetically.' Trippy, man.