The rescues did have a hard start but they live like royalty now.  

 They are among the most spoiled of ducks - and they'll never be mated from a drake ever again.  They do have sexy girl duck time but it's with consent!
Maybe you could put some type of work out mat on the bottom of their coop, over the wire?  Something soft that you could hose off easily?  We used to have bumblefoot issues before we made everything soft so I'm very careful about that.
I don't know very much about what age drakes become sexually interested in girl ducks.  I think it is a combination of season and age that trigger hormones.  I speculate that if it were spring your boys would already be chasing your girls around, harassing them.  So it's possible that you'll have until late winter, early spring when the days are getting longer.  Or it could start anytime.  Personally, I would start looking for a family now so that you won't feel as pressured to take a less than ideal situation for them.
The 3 rescue girls that I took in were on Craigslist for 3 weeks without a single inquiry until mine.  They were young, laying, and free.  It can be hard to find a home for ducks.
I just love that the wild ducks have decided to trust you and hang around!! That is so sweet! They are very adorable.  I quacked at a wild duck flying over once and she quacked back at me.  I felt very fortunate and skilled at quack.