I have a friend who wrote a recently released book. It started as journaling, and turned into a book.
It's called Twins X3 (Twins Times Three).
Yes, she honestly has THREE sets of fraternal twins, one set of each combination. Two girls, boy/girl, two boys. I know some of her story, and I first met her when she was newly pregnant with the 3rd set of twins. I haven't gotten my hands on a copy of the book yet, but it's on my reading list. http://www.twinsx3.com/index.html