I also have broody coturnix quail and have been specifically angling for hens that can hatch their own eggs

It seemed more reasonable to share on this thread than start a new one.
So we've been selecting for size, but more so for temperament in roos and hens alike. Once we had a girl who liked to sit occasionally (no committment) we aimed for her chicks in aprticular for successive generations. I've got NINE of my 28 girls currently who are working together to hatch these eggs, with 5 who really like to sit and 4 more who take turns but also act guard. I made a video about it, a few more things have happened.
Someone, I think one of the two boys, started eating the eggs. I think it was Snowball, because he now has a an injured eye and is staying away from there. They're down to only ten eggs, and we'd found a piece of shell from one of the marked eggs, mostly eaten and trampled. We have too many to relocate everyone, so we tried relocating the entire nest cave and sitting girls to a small enclosure inside the pen (too protect the chicks when they hatch, too) but they were too disturbed to sit. We put it all back and they went right back to sitting, thankfully.
One of the lost eggs got broken by me when we were collecting the other eggs (sorry hens!) and we took that in to see and it, too was developing phenomenally! It was absolutely on track with the ones in the incubator and I've seen the girls turning the eggs. This one's body was about the size and shape of a gummy bear with a long neck and those huge eyes. It was absolutely on track to become a chick at hatching time.
Today is the day I'm putting the incubator eggs down on lockdown, so sometime within the next week those eggs out there should be hatching!
All the other girls are still laying eggs in that nest hole, so I'm a little concerned about kicking the moms off the pipped babies to get the new eggs, but then again the developing eggs get pushed out and lose sometimes, so I can't just leave them for three days. Any advice on that front is most welcome <3
Did any of your hatch,
@Aeswim ?
Here's my video: