Hi I had the same problem last year when my hen had 4 eggs and one had already hatched but the others weren’t even close unfortunately I made the futile mistake of leaving the eggs in with the hen because she abandoned her chick who then died because the hen didn’t support or care for her: you have a few options either make the hard descision of prioritising the first born and getting rid of the other eggs especially if she is a first time mom. Or try donate the chicks to another hen in the hope she will adopt them?
Another possibility is feeding the chick your self to insure she/ he does eat! If you have a heat lamp then you could try and use it if you see the mom abandoning the chick!
You could try and leave the eggs in and hope she cares for all 3, but keep a close eye on the chick! Good luck sorry I couldn’t be of more help! Hope they all hatch