How can I protect my family from harassment?

My wife and I recently decided to leave an organization because we noticed somethings we weren't comfortable with. We just wanted to move on and agree to disagree and leave peacefully. However, the leader of this group called my wife to discuss the situation. He said several things that were offensive, and it kind of became personal, at least for us. We don't think he realized he crossed the line because neither of us reacted right away, and we are not confrontational people by nature. My wife chose to de-friend the leader and the other members of the group she had as friends on Facebook, and I chose to do the same. But both my wife and I got separate emails from this person; the one to my wife was kind of pleasant and contrite, while the one to me was accusatory and judgmental, in reaction to being de-friended. We both felt it was pretty infantile to get so bent out of shape over a de-friending. We just wanted to be left alone. Despite not wanting anything further to do with him or this group, I chose to reply. I cited our offense to the comments he made to my wife, and for the tone of the email he sent me. I did not use any offensive or accusatory language, I just said I didn't appreciate what he said to my wife in the call, and to me in the email. I also told him to stop contacting us. Two hours later, my wife gets an email from his wife which was pretty much a "what did I say?" message. We are not paranoid people by any means (and trust me that in our line of work, we know what real paranoia is), but my instincts are telling me there may be an attempt from other people from this group to try to get us to talk to them. But we don't want to, we just want to be left alone. How do we protect ourselves from harassment from both the leader individually, and from other others in the group? Nothing has happened to this point, but my gut tells me we need to be ready in case someone pushes the line a little further. What can we do legally? How would we prove it? We just want to be left alone, but we fear we are contending with aggressive people, and need some advice on how to deal with them without becoming uncivil ourselves. Thanks for any positive comments.