Make sure your humidity is raised to the 70% range. Some mist the duck eggs, they like plenty of humidity. That does not seem feasible with a mixed bunch. You might place the duck eggs on a damp paper towel. It will dry quickly if you have a forced air incubator. If you can add warm water with at straw or piece of tubing through the vent hole on top. You will not need much just enough to dampen the towel.
My chicks started to pip an peep on day 20.. but didn't hatch till day 21 the eggs were moving on day 18 an 19
my ducks as you no are hatching now as i type....lol
i didn't no what day they started to peep cuz when i got them they already had embryos in them so i just had to keep my eye on them.... all i know is that when they do pip mine took forever to start hatching..lol i'm so glad they are now..