Chick pipped but hen won't sit on it(URGENT)

[RoiKuro]

I had put 12 eggs under a broody chochin and two days ago, 3 hatched. Today the hen is no longer in broody mode and Is now in mother mode and Is leading around the three chicks. The eggs are left behind and one chick externally pipped and I can see it but the mother hen is not sitting on it and giving it heat. I really don't know what to do. It's day 24. I don't have an incubator but I have a greenhouse that is hot and humid. Should I help it?

 

[DobieLover]

I had put 12 eggs under a broody chochin and two days ago, 3 hatched. Today the hen is no longer in broody mode and Is now in mother mode and Is leading around the three chicks. The eggs are left behind and one chick externally pipped and I can see it but the mother hen is not sitting on it and giving it heat. I really don't know what to do. It's day 24. I don't have an incubator but I have a greenhouse that is hot and humid. Should I help it?

When there is a staggered hatch due to eggs being put under a hen on different dates or her clutch being so large that eggs on the outside aren't kept as warm as those on the inside, it's very common for the mother to abandon the eggs that don't hatch within 2 days of the first chick.
You will have to try to hatch the rest of the clutch the best you can and the greenhouse sounds like your best bet. You will also have to brood and raise them as she might not accept them. You can try to give them to her but I would wait until they were 2 days old before trying to slip them under her at night.
I had to assist a late hatching egg that was on the outside of the clutch. She was less than a full day later than her hatch mates. I put her under her mother late at night then checked on them before the flock was off the roost in the morning. Mom went after her twice during the day because the chick was stress peeping because she was cold but the others were active. I intervened and got her back under her mother when the others went under her.
One day late makes a big difference in the chicks ability to tolerate less heat and get out of mom's way when she is teaching them how to scratch and eat. That is why I'd wait until any chick you help hatch is 2 days old before you try to graft them to their mother. Keep the lights on in their brooder around the clock after they hatch, give them their chick starter as a mash and add a little Poultry Nutri-drench to it to jump start them and give them their best chance to be vigorous enough to keep up with the older chicks in the hatch.
Good luck.