Is the marriage contract considered valid if the son married off his father, for whom he was appointed a guardian, to his divorced wife, given that the father did not know the date of the contract and was not informed of it until his death, and is the mother in this case entitled to the legal inheritance, which is one-eighth?

A marriage contract is valid through proxy. Therefore, it is permissible for a father to authorize his son to marry him to his divorced mother. If the contract is concluded during the lifetime of the principal (the father), then the contract is valid, and the father's unawareness of the contract's date does not affect its validity.

Accordingly, the wife inherits her legal share (one-eighth) if there are no other wives. Neither her son nor any of the heirs has the right to deprive her of the inheritance. She has the right to present her case to the Sharia (definition) court.