Beautiful pair you have there!!

And Welcome to BYC!!
Not all hens want to brood. Sometimes leaving the eggs will entice them to sit, but if she hasn't yet, she just isn't in the mood yet. Not sure where you are located, but ducklings in winter can do ok, but I'd wait until spring to try to entice her to brood. So enjoy the eggs! Duck eggs make the best cakes and brownies!
If you want her to sit - you can continue to leave some eggs, and maybe she will decide to sit. Just always have a few fresh ones on hand inside, to swap out the ones outside. You can mark the eggs daily, or every few days. Leave the older ones until she decides to sit (wait till she spends overnight sleeping on the eggs), then swap out those old ones with the freshest ones. If she's your only hen, then 30 eggs would include several that are over a week old, and would be less viable. The freshest eggs will have the best chance of survival.
On the swirled eggs -- duck eggs are naturally swirled. The drake's penis is corkscrew shaped, and the duck's passageway is also a corkscrew, so when the eggs come out, they look swirly. Nothing wrong with that! And most duck eggs are much thicker than chicken eggs, in general. I agree with an "all flock" feed without so much calcium as layer feed, but it won't hurt the drakes on occasion. If you still have some, you can finish it off before you switch.
Best of luck with your beautiful pair!!