What is the ruling of Islamic law on a young man marrying a girl by deception, with the absence of upright witnesses, the guardian (wali), and public announcement (ishhar)? And what is meant by upright witnesses? And who acts on behalf of a deceased guardian?

A marriage that does not meet the conditions of a valid marriage contract is null and void, such as a marriage without a guardian (wali) or witnesses. It is therefore considered illicit sexual relations (sifah) and not a valid marriage (nikah (definition)). The witnesses must be two just men, and the guardian is the woman's father; if he is not available, then her closest male relative.