How genetically close are the parent birds related? Two chicks with the exact same issue have me think of a congenital defect. What you describe makes me think of hydrocephalus, which will only get worse with time.
Please post a picture of the two chicks, so we might be able to assess the situation better.
ETA: It could also be caused by a virus: https://pubmed.ncbi.nlm.nih.gov/20408417/
Please post a picture of the two chicks, so we might be able to assess the situation better.
ETA: It could also be caused by a virus: https://pubmed.ncbi.nlm.nih.gov/20408417/
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