At this point I would plan to get them like I would rescue abandoned ducklings on a pond. Get a few friends, some temporary poultry fence (50 feet of it), and either waders or a kayak or something that safely floats.Ok, we let our two duck out of their pen for the first time four days ago and the one flew in my pond. So my daughter caught the other duck and put him back in the pen. Then the one that flew in my pond came back. So the next day I let them both out again. The same one flew back into my pond. This time I caught the other one and my son wanted me to put the second one in the pond, so we put did. This time they didn't come home it's been two days and two nights. I can see we're they are now. Does anybody know how we can get them out of the pond. I'm afraid something will get them. They are only two months old.
The fact that they fly is not going to make it easy, as you know, but if you can get them between you and the shore, then move toward them, you may be able to coax them into a temporary fence on the shore. With a few extra hands, you are likely to be able to bring them in.
And then try again with the wing clipping and convincing them where night-night home is. Give them treats lavishly only in their night pen. Perhaps you may feed them only in their night pen - but make the food available 24/7, as they are still ducklings.
See if you can give them something to do or play with in the pen. A nice pile of compost that draws worms is great sport for my runners. And the compost doesn't have to be stinky old kitchen scraps. You can layer chopped straw and a little lettuce, and worms will start to show up. Just stir the little pile every few days.