Final update:
The chicks are doing really well, growing so fast, full of energy, and just being cool chicks. Mama hen is an amazing mama, attentive, protective, and gracious. Every day she takes them out for long walks around the garden, finding food, and giving it to the chicks showing them how to forage and bathe etc. Occasionally she'll happen upon her favorite treats hidden in the grass and it's so nice to see her not gobble them up but to break the treats into smaller pieces and offer them to her little ones. Watching them devour an entire banana was the funniest to watch as they clambered over each other and the banana to get the little bits out of mamas beak, but completely ignored the banana itself
For me and our household, watching this all is genuinely a first. My wife, who had real issues handling any animal, even cute ones, is now actively involved in caring for and managing the clutch of 11 wonderful little furballs and their mama hen.
And sadly, that number is where it will remain. The last egg was chirping away yesterday as it had pipped internally, and we were all looking forward to it hatching, however, 18 hours passed and I got worried it hadn't pipped externally. I candled the egg, located a safe spot to make an entry, and peeled back the eggshell piece by piece to find the little one had already passed. I'm confused as to what went wrong. The yolk was absorbed, navel closed as it should be. Nevertheless, it's the end of this chapter, and a new one begins.
Thank you all for your advice and support. Hopefully, there is plenty of info here for anyone ending up in the same predicament.
Watch the above video, it shows all of the chicks with their mama hen. The kids have been showing the videos to their class and the teachers have asked for regular updates, so the youtube channel has inadvertently become a chicken channel. Will continue posting videos of them there.