I am trying to make the Wilton Class 3 final cake tonight and cover it with fondant. I have made 2 batches of MMF. Do you think that will be enough to cover a 10 inch cake and a 6 inch?

Not real sure, but it might be closer to 2.5 batches. Depends on how thick you do it. I would probably do three just to be sure you have enough and you can always save the rest for another cake or for decorations.