You should not have any problems or concerns about the movement of the frog(s) at
this point. Collect some water from the tank, and move the frog(s) in the water to a nearby pond which does not completly freeze. A small pond vs. a large lake is the better choice in my opinion. Your visitor(s) have migrated to your barn, and are tolerant of native conditions. Do not attempt to keep them out of water for more than that which can be understood as needed. They should be fine. The sooner the better.