Yes your flock will attack them unless you put them under a broody hen in the night and even then it is a gamble. I would brood them separately until they are at least 7 weeks, if possible in the corner of your coop with them in a dog crate so your other girls get used to seeing them.
I would personally wait on putting nest boxes in until they are closer to laying age. If you already have them in the coop I would block them from use. It's a bad habit for them to learn to sleep in the boxes. No one wants poop covered eggs.
Scratch is like candy, only in moderation. Roosters do not need the extra calcium in layer feed, it will shorten there life expectancy. If you have roosters preferably you should feed an all flock with oyster shells in a seperate feeder for the hens to eat as needed.
Sweet PDZ is an odor helper made for horse stalls. You can find it at feed stores, great stuff. I sprinkle it in my deep litter coop whenever I feel the need.
Could you add some greens or hay to the mix of grains you are providing? Also soaking the bigger grains for the babies will help them to be able to eat it.
Del's had straight run assorted ducks this week. They where all Pekins except these 4. I looked on Metzer and they looked like black Swedish ducklings, but wanted a second opinion.
I also would do deep litter. We use horse pellet bedding or fire pellets without ignitor. We sprinkle our wood ash in there and in the dust bath tires, and speinkle the occasional DE and Sweet PDZ. You only have to clean it once a year or so, which I am sure some teen in your area will do for a...
Easter Eggers are the name for Ameraucanas that are not purebred essentially.
I agree, the smaller ones look more chipmunky to me and I would count that as your Easter aEggers, maybe they are bantams? Or are just different ages.