I think
Sally gave fabulous insight, as always.
The only other thing I might add is to peek at a few feathers under a magnifying glass if you have one.
Whenever you have possible plucking or feather loss, you want to check for feather mites.
It's pretty easy. It's easiest to see on tail feathers or flight feathers. (Shed ones are easier vs trying to examine them on the bird.)
On the underside of the wings, it may look like mold in severe infestations on a light colored bird.
But few cases are severe. It's usually really subtle, but it can cause itching and plucking.
Usually, it's right along the center as small dark colored or light colored dots (the light or dark appearance of the mites will depend on the feather color, whether they've been feeding and the precise variety.)
On some of the smaller, fluffier feathers, it can look like tiny dots and they can take on a moth-eaten look when you look closely.
If you hold it up to a bright light, you can see the color differential in some more severe infestations:
Here's a good pic of how they look under magnification; it helps you see how they tend to accumulate:
It's probably not the case here, but I thought I'd mention it just in case. It's something to be aware of and consider whenever you have plucking or feather loss. A couple cases where I saw feather mites, the birds had started plucking around that same area - the sides, mostly to the rear. (Not sure why. Perhaps it's just one of the easier spots to reach?)
Honestly, though, as Sally said, if they're eating, sleeping and pooping normally, I wouldn't be too worried.
It's hard to tell in the photos, but the skin looks healthy in the bald spots, which is another good thing.
I'd just chalk it up to being plucky due to nesting.
