Can you separate them? If you have two nesting sites available, try removing Grandma and letting the other Mama's babies run to her. Once they divide themselves up naturally, you can contain each family separately. It may only take a few days/nights of "enhanced division" before they start doing it themselves. Ducklings can be quite persistent once they've decided where they belong!That's funny! But 25 is still so many so i'm hoping at some point she allows the other Mama to help her out. She was dozing off earlier in the sun today while the 25 ducklings were all scattered about her so she's going to need help or they're going to get picked off quickly.