Do you have chapter advisors? Having them write a letter with e-mail addresses and phone numbers for questions would be beneficial. Also, holding Mom's Day or Dad's day for the parents to visit and see "what it's all about" may be helpful. Unfortunately it seems like we have to battle a lot of untrue stereotypes so the goal is show the positives of being greek. And obviously there are many, so this shouldn't be too hard!
I know that what was especially important to my family was knowing about alumni connections and how this may be help a new grad find a job!