how long do eggs stay good?

I've got two people that want duck eggs from me, one lady wants 2 dozen mallard eggs for her kids to incubate, and another lady-a teacher wants two dozen of whatever eggs I can give her.

I've got 10 mallard eggs from Tal that she never started setting,

the thing is, the two people don't want the eggs til the MIDDLE of april.

Tal has completly stopped laying, and I'm not sure why.

but could it be possible to save these eggs, and have them still be good in april??