(1) A child does not become one’s own and real son due to adoption. And the adopter does not become real father and the adopted son does not become his lawful heir. If someone adopts a child with the intention to become his real son and lawful heir, it is not right. It is unlawful.
(2) Don?t worry; this Nikah is valid according to shariah.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband