Search 'EGGBOUND' here on BYC.. use the Search option here to get info on Eggbound... You need to check them and treat them if they are eggbound... so you don't lose them.. the one sitting will be fine.. if she seems well otherwise.
I don't know how old your hens are... but, younger hens, new layers tend to get eggbound more it seems.. until they get more experienced at it.
Depending on their ages... use the search here... immediately check and treat for "eggbound".. and let the one sit on her eggs that is sitting, if she has no other problem. She will get off the nest now and then.. sometimes not for a couple of days.. but, she should get off to eat and drink and poop...
I would bring the other two in -- the head down, bum up ones.. and check them over.. keep them warm.. see if they are eating and drinking..
Use the search here for "giving oral medications".. "giving food and water by mouth"... "giving food and water orally".... "feeding a sick chicken".. and, as I mentioned... check for eggbound.. sitting on the nest is the pointer to a laying problem on the two that are sitting .. BUT... a hen can go broody and have no eggs to sit on.. they will sit on anything and even an empty nest... so.. . check them out -- if they seem well otherwise, or get better and go back to the nest.. you might want to divide up the eggs and give each one some of them. You MIGHT have three broody hens at the same time?
Good luck... best and more info can be found here on BYC by using the search option. I hope they are fine and all comes out o.k.
