All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
We have already issued Fatwa 86395 clarifying that a husband is not obliged to inform his second wife that he is already married. Therefore, you have no right to file a case against that man just because he was already married before marrying your daughter.
As regards what you mentioned about his mistreatment to your daughter – if this is true – then he is Islamically not permitted to do so as he is ordered to treat her kindly; Allaah Says (what means): {And live with them in kindness.}[Quran 4:19] For more benefit, please refer to Fatwa 88304.
In case she is harmed by staying with him, then she has the right to ask for divorce due to the harm even if this divorce is in return for compensation that she gives to him; this is what is called Khul’ and it is clarified in Fatwa 89039.
However, it should be noted that he is not permitted to take this compensation from her if he is the one who caused the harm. Allaah Says (what means): {And do not make difficulties for them in order to take [back] part of what you gave them unless they commit a clear immorality [i.e. adultery].}[Quran 4:19]
As regards the fostering of these two children when the parents are still married, then it is the right of both parents, and if they separate, the fostering is for the mother as long as she does not remarry. In case she travels to another country, the fostering is for the father; Al-Mardaawi from the Hanbali school of jurisprudence, said in his book “Al-Insaaf”: “If either parent wants to travel to a distant and safe country in order to live there, then the father has more right in fostering the child.”
Moreover, Ibn Taymiyyah said in his book “Al-Fataawi Al-Kubra”: “If the husband resides in a country other than the country of the mother, then it is him who has the right in the fostering and not the mother, even though the mother has more right in the fostering than him if they are in the same country. This is also the view of the four schools of jurisprudence.”
Furthermore, having a bad conduct does not prevent the father from his right in the fostering as long as the matter does not reach dissoluteness as the fosterer may lose his right in fostering due to this, like if he/she is known for committing Zina (fornication or adultery), consuming intoxicants and the like. For more benefit, refer to Fatwa 90461.
As mentioned before, your daughter has the right to ask her husband for Khul’, meaning asking him to divorce her in return for compensation that she gives to him. In case she takes Khul’, she becomes irrevocably divorced from him, and so, he does not have to spend on her unless she is pregnant. Besides, she is obliged to observe a waiting period and she is not permitted to live with him in the same house unless each one of them is in a part of the house that is separate with all its amenities as he has become a non-Mahram to her and there is no longer any relation between them.
In conclusion, you may endeavor to free your daughter from that man if it is confirmed that he harms her and she wants to be separated from him. Nonetheless, our advice is that rational people from the family of the husband and from that of the wife should interfere and try to reconcile between them if possible, otherwise let separation take place in kindness.
It should be noted here that it is not permissible to take the case to non-Islamic courts unless in case of necessity. Similarly, it is not permissible to act according to its ruling if it contradicts the Sharee’ah.
Finally, the following two matters should be noted:
1- The scholars differed in opinion in regard to a husband preventing his wife from visiting her parents even if they are in the same country, let alone if they are in another country. For more details, refer to Fatwa 82969.
2- What you mentioned about that man accusing you of trying to kill him, if this is just an accusation without any evidence, then this is a clear sin; Allaah Says (what means): {And those who harm believing men and believing women for [something] other than what they have earned [i.e. deserved] have certainly born upon themselves a slander and manifest sin.}[Quran 33:58]
Allaah Knows best.