Is it obligatory to conceal the fact that a girl of unknown lineage was adopted and attributed to the family, or should she and her husband's family be informed of this, knowing that there is no information about her true lineage?

The girl and her husband must be informed of the reality of her adoption, because their ignorance of it leads to Sharia (definition) violations such as shaking hands, being alone, and seeing non-mahrams, in addition to the rulings of lineage concerning marriage, inheritance, wala’ (allegiance), and maintaining kinship ties. The appropriate manner of informing should be observed so as not to hurt the woman's feelings, clarifying that she has no fault in this, and that the husband must support her in accepting the matter.