The thing is, you can only do so much. You can prepare beforehand, maybe by writing it down, what you'd like to say and what points you feel you need to make (this helps me because then I don't get upset and forget to say something). You can calmly tell them how you feel and what you think. But the rest is up to them, and frankly, they do not sound reasonable to me.
I would think about what you want to get out of the meeting. Do you hope to establish good relations between everyone? Keep in mind that takes both parties to work for it and want it. It will not work if they don't want it to work and are there to attack you, no matter what you do.
If I were you, I would not expect them to take responsibility or apologize. I would simply say, "I'm sorry for offending you. Do you accept my apology?" Hopefully they will say yes, and you can say, "Thank you. I'd like to move on from this issue, then, and put it behind us. Is that okay with you?" Again, hopefully they will say yes, and everyone can go on with their lives.
Honestly, I'd just completely block them both on Facebook and leave them alone until they decided they wanted to mend the relationship, but I know that isn't reasonable in every case.