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, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
Firstly, the scholars stated that in case of divorce, the wife is entitled to the custody of the children who are under seven years old, provided that the mother is able to achieve this and there are no impediments in her. For more details, refer to Fatwa 84618.
Secondly, different views are provided by Imaams of the four Schools of Fiqh regarding the time when the mother's custody of the children ends. Al-Khiraqi said: "When the girl reaches seven years old, the father is more entitled to her custody." Commenting on this, Ibn Qudaamah said in “Al-Mughni”: “Ash-Shaafi‘i said: ‘Like the boy, the girl should be given the option (to choose between living with her father or living with her mother), because she is entitled to the same rights of the boy in choosing." Abu Haneefah said: "The mother is entitled to the custody of the girl as long as she is still unmarried and or did not reach the age of menstruation." Maalik said: "The mother is more entitled to the custody of the girl until she marries and the husband consummates marriage with her.’”
Thirdly, the scholars stated that the parent who has the custody of the children is not entitled to prevent the other parent from visiting the children. In “Al-Mughni”, Ibn Qudaamah said: "A parent should not be prevented from visiting the child who is in the custody of the other parent."
If the mother's right to custody of the girls has been approved and she does not allow her ex-husband to enter her house, she should bring them out at the door so that he can see them. Nevertheless, if there is no sound reason to prevent him from entering the house, the wife should not prevent him because he is the father of her daughters. An example for the impediments that prevent the father from entering the mother’s house is; fearing temptation because of the daughter’s father entering upon his ex-wife at a time when there are no Mahram men in the house. For more details, refer to Fataawa 84575 and 89876.
Fourthly, what you have mentioned that the father kidnapped his daughters is unclear and we do not know what led him to such an action. Generally, a father is merciful to his daughters and therefore it is not expected that he harms them. As long as the issue has been taken to court, it can investigate it and its judgment must be binding as long as it judges according to rulings of the Islamic Sharee`ah.
Fifthly, the father is required to financially maintain his daughters if they are in a state which requires that. Nevertheless, neglecting his duty of financial maintenance does not prevent him from visiting and seeing his daughters.
Sixthly, as regards the father’s calling his ex-wife a disbeliever, if she indeed admits to that, this makes him more entitled to the custody of the girls. This is according to the preponderant opinion of scholars. However, if she does not admit to being a disbeliever, in such a case what he says is a mere claim and he is required to bring evidence before the court, otherwise his claim is rejected and he deserves the discretionary punishment, so that people would not take lightly labeling others as disbelievers without evidence.
Finally, we draw your attention to the fact that the issue of custody is one of the serious matters and there could be many unverified claims about it. A judge who judges according to the rulings of the Islamic Sharee`ah is worthier to investigate such issues and Fataawa are not enough. Moreover, many of the custody issues are subject to difference in opinions among the scholars. So, the judge's final decision settles difference in the Ijtihaad-based issues and his judgment is binding for the two parties. However, if the parents can make reconciliation to do the best for their daughters, this would be better, because such disputes have a negative impact on daughter's life.