What is the ruling of Islamic law regarding a man who divorced his wife twice, and she has not yet moved into his house, and how can she be returned to him? And is his oath of divorce permissible?

One must distinguish between a fiancée (who has not yet had the marriage contract [aqd] solemnized) and a wife (who has had the marriage contract solemnized), as each has different rulings.

If she is a fiancée, he is not permitted to be in seclusion with her or to address her except out of necessity. If she is a wife but he has not yet consummated the marriage with her, he can remarry her with a new contract after a divorce. However, if he has consummated the marriage with her, he is permitted to take her back without a new contract during her waiting period (iddah) if it is the first or second divorce.

If the divorce is an irrevocable divorce (bainunah kubra) (three divorces), she does not become lawful for him again until she marries another man and is subsequently divorced by him, provided that the second marriage was not intended solely to make her lawful for the first husband (tahlil).

It is recommended to refer to the Sharia courts to resolve these complex matters.