They don't know. There are very few users that I told my family about (with the exception of Krazen and Barfbag).
I think it's time you sat your parents down and said "Mom, Dad…..I've been hoping to delay this conversation as long as possible, but I think you deserve to know now. You'll hear it from someone eventually, so better that it come from me. (long pause) There are other posters on the Atlas forum that you need to know about, and the first one is named 'opebo'."
LOL! I think my mom only went onto the forum a few times, as I told her about some of the alternate history timelines. I don't think she looked at the forum community or individual politics threads while she was on the site though.