They see you as mom. So, I would but them in the seperate pen and then either sit in or next to the pen or do yard work near by. Decrease the time you stay neaby each day. You are trying to teach them that you are all members of the flock which includes the big ducks. Then, when they are...
They can take 48 hours from external pip to hatch. They would only be hatching a day early then. Your temperature or humidity might be a little high. Ducks take longer than chickens to hatch after pip.
Exercise! Specifically swim therapy. Get that baby swimming in the bathtub several times a day.
You can also give it Durvet’s B vitamins. It is made to be injected but instead squirt a mL worth over a treat like meal worms and feed it to him. It will give him extra niacin. Some just need...
Were the large eggs double yolkers? Young ducks often lay them early on and then settle in to laying regular eggs. When they get older the eggs will get bigger but not as big a one with two yolks.
If the big eggs only have one yolk, the other eggs may be a different duck?! 🤷♀️
I have used it with success from hatch. I crumble it in my food processor and add water for the first week. Add extra nutritional yeast if you are worried about niacin.
Be aware that ducks are not as like chickens as some expect. They love water and mud all the time and need water deep enough to put their whole bill in. So, chicken water nipples will not be good for them. Their water stays clean for about 10 seconds before they drop food and dirt in it. Any...