As I understand it,
Dual-gender is a type of gender fluid, where the identified gender changes between two different identities. Most commonly, the dual gender person would identify as male for a few days/weeks/months, but then their gender can switch to another identity. It differs from genderfluid on the whole, because dual gender people switch back and forth, where genderfluid people, they're identities doesn't seem so neatly defined.
Androgynous is not a gender identity. Instead it's a gender presentation. A person who is androgynous cannot be easily distinguished as male or female. Think Andreja Pejic, especially when she would present as more masculine leaning.
There is a type of genderqueer gender identity I have heard referred to as "Androgyne" - literally man-woman. Most often, I have seen this one described (pardon the reductionist view) as a woman downstairs and a man upstairs. There are definitely other genderqueer identities, but androgyne is just one of them.
Another author shamelessly promotes self-written fictional short story in which the main character is bigendered: http://www.wattpad.com/story/36482852-miss-mississippi
^^mods, ^^please ^^let ^^me ^^know ^^if ^^this ^^isn't ^^allowed ^^and ^^i'll ^^remove ^^it
Yes! I couldn't tell if le Guin was letting her bigotry show, or if she was masterfully crafting a character from a cis-patriarchal world. She really captured a lot of my subconscious bigotry when I first learned about trans people. The only reason I wonder if le Guin has subconscious bigotry is because I read an (essay)[https://getpocket.com/explore/item/ursula-k-le-guin-on-being-a-man] of hers in the book "the wave in the mind" and I couldn't tell how much of it was 'woke' commentary and how much of it was self-aware misogyny.