This is a bad situation of lesbian induced accidental incest. I don't want to go all spoiler warning on you so just check it out from Slate Magazine:
Q. Nasty Surprise: When my wife and I met in college, the attraction was immediate, and we quickly became inseparable. We had a number of things in common, we came from the same large metropolitan area, and we both wanted to return there after school, so everything was very natural between us. We married soon after graduation, moved back closer to our families, and had three children by the time we were 30. We were both born to lesbians, she to a couple, and me to a single woman. She had sought out her biological father as soon as she turned 18, as the sperm bank her parents used allowed contact once the children were 18 if both parties consented. I never was interested in learning about that for myself, but she felt we were cheating our future children by not learning everything we could about my past, too. Well, our anniversary is coming up and I decided to go ahead and, as a present to my wife, see if my biological father was interested in contact as well. He was, and even though our parents had used different sperm banks, it appears so did our father, as he is the same person. On the one hand, I love my wife more than I can say, and logically, done is done, we already have children. I have had a vasectomy, so we won't be having any more, so perhaps there is no harm in continuing as we are. But, I can't help but think "This is my sister" every time I look at her now. I haven't said anything to her yet, and I don't know if I should or not. Where do I go from here? I am tempted to burn everything I got from the sperm bank and just try to forget it all, but I'm not sure if I can. Please help me figure out where to go from here.This is an excellent reason not to get involved with artificial insemination.
A: This is a seminal question about the nature of assisted reproduction. As David Plotz discovered in his book, The Genius Factory, on the alleged sperm bank of Nobel Prize winners, many non-geniuses were moved to spread their seed far and wide. So the question has always hung over this: What if the offspring meet and fall in love? Well, you've met and it's true that if you had researched your origins and disclosed them to each other, you and your wife would now likely be close half-siblings. I understand your desire to burn everything. But if you are now looking at your wife and thinking, "Hey, sis," I don't see how you can keep this information to yourself. She's bound to sense something off in your behavior and you simply can't say, "I'm struggling with father issues." I think you have to sit her down and show you what you've discovered. Then you two should likely seek out a counselor who deals with reproductive technology to help you sort through your emotions. I don't see why your healthy children should ever be informed of this. That Dad didn't want to find out who his sperm donor was is a sufficient answer when they get old enough to ask about this. I think there's way too much emphasis put on DNA. Yes, you two will have had a shock, but when it wears off you will be the same people you were before you found out. Shocking news has the effect of making people feels as if the waves it sends out will always rock them. But I think you two should be able to file away your genetic origins and go on.
While this might seem like a cautionary tale to many, this will probably be used as a boon for the argument that people should be allowed to marry their siblings. And if you're against it, you're just hateful.