I'm so sorry for the circumstances that brought you here.
I bought four ducklings earlier this year. I had one that started to have seizures. Thanks to the folks on here, she made a full recovery. It was Niacin deficiency. Once she got some niacin, she was back to normal and doing fine today.
There isn't more to add to the advice given other than to say make sure their drinking water is warm, not cold.
Good luck and keep us posted.