Call ducks breeding this time of year?

One of my ducks have been laying pretty steady this week, and I just witnessed another one being bred.. (How to explain to a 5 yr old child that its ok for them to be fighting in the pool??? LOL)

Is this normal? I thought they were an only once a year type??

And if it is normal, I need to move them away from the chickens so the chickens dont run them off the nest.. Ive already gotten a chicken egg from the duck nest...

Now for other questions... Will they set the eggs themselves?? I didnt give them a chance earlier this year and incubated them in the house. How many will she lay before she starts to sit?

And when I seperate them from the chickens, can I move the eggs she already layed and put them in a spot I want her to lay?? I dont have a duck house, but Im going to use a realy large dog igloo with shavings for them..

I already put a couple of the eggs under a chicken thats trying to set, but im not holding my breath on those..