What is the ruling regarding a wife returning to her first husband, who apostatized and then repented, after she had married another man, especially given that they have a child together and reside in a country where there are no Sharia courts?

If the second man marries a woman while she is still in her waiting period (iddah) from the first, his marriage is invalid, and she must separate from him.

If the first husband returns to Islam while she is still in her waiting period from him, she returns to him with the first marriage contract, and he should not approach her until she completes the iddah from the second man, if he had consummated the marriage with her.

If he returns to Islam after her iddah from him has expired, then a new marriage contract is necessary, and this is the more sound opinion to avoid the disagreement of the majority of scholars.

However, if the second man marries her after she has completed her iddah from the first, then his marriage is valid, and neither she nor the first husband has the right to annul it.