Family and intimate imagery
Because of an unsavory prophecy, this Duke moves his family to a summer home in the country where they will wait out the activity of the gods. Their time there is intimate and somewhat tiresome. The constant over-exposure to each other makes the family imagery rise to the foreground while civilization falls away. They are far away from any other people they know, so when things start to get sexual and freaky, the intimate aspects of that are free to soar.
Natural imagery
The presence of nature in this story cannot be ignored. A subtle psychological argument is being made about the metaphysical reality of gender dynamics and the sexual ecstasy of uniting opposites. This is very erotic-sounding language, but in the context of the remote wilderness, amongst the many animals that surround the family, the erotic passion is shown as animal. When "Zelmane" wiggles "her" way into the family's hearts and minds, that might seem unnatural, but Pyrocles is clearly an instinctual person. His feminine prowess is part of his natural personality.
Personality play
The idea of playing one's self is symbolically associated with masquerade and costume, so the reader can thank the gender-bending Pyrocles for highlighting this imagery. By pretending to be a woman, Pyrocles accidentally makes everyone fall in love with him. This is because he is a highly instinctual and intelligent person who understands people's desires because he is in tune with his own desires. He knows that a direct approach will not suit this paranoid family, so he masterfully performs an acceptable personality. He sells the part because it is not a lie; he is truly very feminine.
Femininity
Every character in this play is a portrait of femininity. The most masculine players in the cast are Duke Basilius and Pyrocles, but Pyrocles dresses like a hot young lady and accidentally seduces Basilius. Why is Basilius attracted to Pyrocles if Pyrocles is obviously kind of masculine as far as "women" go? The answer is that compared to the aged and experienced experience of Basilius, Pyrocles (even at maximum masculinity) is feminine. That does not mean they are not simultaneously masculine; they are masculine enough to be magnetic and charismatic in a family of thoughtful and considerate women.
