Oh God Tarraann you poor person!
I truely feel for you 2 cats and all those babies.
My best guess would be they were likely dropped off together, bet them kittens warmed right up to you right?
if so they hadn't been born out there.
I wish I was closer I would pick up both moms and litters , I have people waiting for kittens and all mine are spayed but 1, 9 month oldish and is knocked up higher than a kite, but those kittens have homes and more people are waiting for kittens.( she was someones dump off also). I am still trying to catch the big black and white male that arrived around the same time she did.
I feel for you I truely do,
Is there any way you can contain the scovie with the eggs untill momma cat and kittens can find new homes?
Maybe a make shift pen of sorts, I know its unfair to the duck to be penned while a strangers cat well basically takes over her home turf, but it will be safer for the ducklings when they hatch.