1000 years ago, the Karaite communities of Ramle and Jerusalem probably would have excommunicated my grandparents.
You see; my maternal grandmother and her sister married my maternal grandfather and his brother, respectively. Two brothers married two sisters (in separate marriages).
I always thought this was beautiful. But from at least the time of Anan and for several hundred years thereafter, the majority of Karaites forbade many types of marriage, including the marriage of two brothers to two sisters.*
And, according to a piece appearing online at the Jerusalem Post this past weekend, some of the Karaites of the 11th Century had no problem tormenting Karaites who violated this prohibition. (See A Problematic Marriage for 11th Century Karaites.)