Can Identical Twins Be Different Sexes?
Sex differences in the fetal heart rate variability indices of twins. - Abstract - Europe PMC
At least it seems that way, judging by the number of reporters calling me to ask about the sex lives of conjoined twins since the TLC reality show Abby and Brittany went on the air several weeks ago. But not as conflicted as we singletons seem to feel about them having sex. Typically, people who are close to conjoined twins come to adjust and see them as different but normal; they seem fairly untroubled by the idea of conjoined twins pursuing sex and romance. But those who are watching from afar cannot abide. Chang and Eng were joined by just a bit of liver and some skin.
Monozygotic twins of different sex.
Incest between twins or twincest is a subclass of sibling incest and includes both heterosexual and homosexual relationships. Sexual arousal from a twin sister or sister in general is referred to as sororilagnia or sorophilia , while a male analogous term is fratrilagnia ,  and a more general term is sibcest. In traditional Balinese culture, [ when? The standard anthropological explanation of this custom is based in explications of the conflicts between descent and affinity in Balinese society.
Every parent of twins faces the question "Are your twins identical or fraternal? Many think that being identical twins refers to how twins look and not how they form. Take a look at the biology that determines the sex combinations that are possible with identical and fraternal twins. The terms identical and fraternal don't describe what the twins look like, but actually how they form.