Well, I don't know how well known it is in my family, but I have only brought it up to my close family. My step mom is anti-circ but she never informed me until after DS#1 was cut and I realized it and started feeling guilty. Then she said "Yeah, I never wanted to circ J, but your dad really wanted it done. Thankfully we chose to wait until his 1 week visit, but because of what happened he never and go to through it." Her son, my half brother had a heart condition and passed at 3 weeks, so they didn't have it done since they knew he wouldn't make it. I just wished she had shared this with me BEFORE I cut DS#1 since in previous conversations she had mentioned that maybe I should wait until his 1 week check, but never mentioned just not doing it! I never realized we could just not have it done. Anyways, she was very happy we we didn't have it done and gave me props for taking a strong stand against DH. When DS#2 was born she asked if I pushed his foreskin back to clean at every diaper change or just in the bath, I told her never, your not suppose to.
My sister was totally supportive. We had talked a lot and I gave her a ton of info on why it wasn't needed and how horrible it was. I don't know how strongly she feels about it, and I am not sure if she will take a stand against her fiance, but she isn't very likely to be able to physically have children.
My mom just rolled her eyes and said "Oh, I am suuuure you researched it and KNOW that is the best. *sigh*" I told her that yes it was the best and yes I did do a lot of research and I would NEVER do it to another child. She was like.. whatever...
My MIL just said "Are you EVER going to do it?" I said very nicely "nope, and you are never suppose to pull back the foreskin." she just said "Ok" and that was that.
I have no clue how my dad feels, I don't think he cares. He just loves his grandsons and thinks they hung the moon.

I haven't talked to my brothers, but they are still pretty young (17&19) and we don't really get along and they aren't really interested in parenting or anything to do with it. LOL They love their nephews but could care less about circ or breastfeeding or anything like that.
My BILs I don't know, I don't know them very well and they are both circ, but are also very young (16 &17).
My extended family, I think all the boys are cut, but we don't talk about it, I don't see them very often because we live so far away.
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