What is the ruling on adoption in this case, and what should the husband do, knowing that he raised his ex-wife's daughter from when she was three months old, and his brothers treat her as their niece, and she does not observe hijab in front of them?

Adoption must be abolished because Islam has nullified it, and the husband must repent if he knew his action was unlawful. The girl should be attributed to her known father; otherwise, she should be attributed to a general name like Abdullah. The girl should treat the husband's brothers as strangers after reaching puberty, while the husband is a mahram to her due to his marriage to her mother if he has consummated the marriage with her.