I've moved babies days after the others hatched. It's the only thing I can think of for them.
I can just imagine the others' reactions! Thankfully, my group seems to be fairly good about the ducklings, ignoring them for the most part (which also means stepping on them sometimes *sigh*)...
No idea what goes through their heads sometimes. Hopefully you'll be able to save the remaining ones.
Maybe try to sneak the babies in after they hatch with the mothers after dark?