Do I really need a comforter/quilt for my babies' cribs?

No you do not need a comforter/quilt. You are never suppose to use them in their cribs so it would be just for decoration. Which to me is a very expensive decoration to have. You can just buy a couple of soft blankets for your babies to lay on the floor with during the day. The blankets in the link you provided are very nice blankets. congrats on your twins!