If you wish to legally adopt your elder brother's 10-year-old son, a formal Adoption Deed is recommended. This deed should be executed by you, your wife, and your brother and his wife. Without formal paperwork, the child's parents could reclaim him at any time, and you would have no legal claim. While the Hindu Adoption and Maintenance Act doesn't mandate a deed, a registered document provides legal presumption of validity. The core legal requirement for adoption is the physical act of giving and taking the child between the natural and adoptive parents.