Identical twins should have the same sexual orientation. The gene Xq28 influences same sex attraction men.
It comes from the mother’s genes. But because there are lesbians, that means that there could be a gene from the father as well.
Because of this, it proves that there’s a gene that does cause same sex attraction that would be inherited by identical twins. Identical twins share 100% of each other’s DNA. They would have the same sexual urges towards the same sex. If they don’t show signs of same sex attraction, they could be not truly identical twins, or they are suppressing their attraction.
Another way that twins could not have attraction towards the same sex is if Xq28 was not activated. Since Xq28 isn’t found in every individual, it could be a genetic mutation. Mutations are not always activated in offspring. Therefore, having identical twins with different sexualities is not possible.