Answering the question, Sheikh `Abdel Khaliq Hasan Ash-Shareef, an eminent Muslim scholar and Da`iyah, stated:
Adoption in the sense of changing one’s identity and lineage for a false lineage is prohibited in Islam. Almighty Allah says,
“Proclaim their real parentage. That will be more equitable in the sight of Allah. And if ye know not their fathers, then (they are) your brethren in the faith, and your clients.” (Al-Ahzab, 33:5)
Therefore, this man is not allowed to be named after a father other than his real father.
as for the marriage to him, there is nothing wrong with it.
May Allah guide all to what pleases Him!