How sad it is that someone was so cruel as to leave them in a plastic bag on the road. They are lucky you found them. If you release them they will no doubt die from being preyed upon, or perish due to not knowing where and how to forage well. Can you take them to someone who already has ducks? We have a livestock auction here in Erie, PA where people sell ducks and other animals. Can you sell them or give them away on your areas FB Marketplace or Craigslist? PLease put some effort into finding them a new home, they will appreciate it, and thank you for caring for them..