You may want to consider that apologies can be more receptive if you consider the timing. They may need a short time to digest what happened but will come around after they have time to think. When you apologize include that you treasure your friendships and make sure that it is sincere. Give them a short time to get past the exchange. They may be willing to do things in a few months that they are not willing to do now. You may want to consider a letter which can be more personal than Facebook. If you find they are receptive then give the reasons for your anger. I think if they are true friends they will eventually forgive you.