It's not usual for authors to write in pairs. Everyone knows the Brothers Grimm, and, ummm...
Writing is such an individualistic endeavor, after all. Here you are, staring at paper/typewriter/computer, trying to get your OWN voice out. That's hard enough. But having to share it with someone else? And then trying to mend your voices into one homogeneous narrative? Why make life even more difficult?
Perhaps it was done best by the pair of Ilya Ilf (Jew) and Evgeni Petrov (Sadly, not a Jew). The duo penned one of the most wonderful pieces of Russian literature, "The Twelve Chairs". Ilf wrote a third, Petrov wrote a third, and a third they wrote together.
But even with these two, it wasn't all harmonious. At the end of the novel, they had a huge fight of whether to kill the protagonist, Ostap Bender. The writers settled it in the only way possible: they drew lots. Bender got his throat slashed... only, in perhaps the ultimate compromise, to be resurrected three years later in the equally brilliant sequel, "The Little Golden Calf".
So no, we don't know how we do it. Some of these profiles are written by one person, some by the other, and some are a mixture. We guess that we couldn't help but...
Hey, what are you doing? Don't edit that! STAY AWAY FROM MY PROFILE!!!!!!!!!!!!!!
... learn to compromise.