Is a marriage considered valid if the contract was concluded before a lawyer without the presence of witnesses at the time of the عقد (marriage contract), with an agreement for them to sign later based on the lawyer's pledge that the marriage would occur, and is their later signing and photographs of the couple sufficient for the validity of the contract and the nikkah?

Marriage without a wali (guardian) is invalid according to the majority of scholars, and there is no distinction in this regard between a minor and an adult, or a virgin and a previously married woman. Witnessing is a condition for the validity of the marriage contract, and it should be at the time of the contract such that the witnesses hear the ijab (offer) and qabul (acceptance). If the contract was concluded without a wali and without witnesses, it is invalid, even according to the Hanafis. Therefore, you must separate from this woman, and if you wish to marry her, it must be a valid, lawful marriage conducted by her wali or his agent.