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.
It is not permissible for anyone to force two spouses to separate through divorce or Khul’ without a Sharee‘ah-based reason. It would not even be valid unless they consented to it. Rather, this is like what the sorcerers and devils do when they work to separate loved ones. This causes Fitnah (tribulation) in the earth and great corruption. Allaah The Exalted Said about sorcerers (what means): {They then learn from them that by which they cause separation between a man and his wife.} [Quran 2:102]. It is reported in Saheeh Muslim that one of the troops of Iblees (the Devil) says to him: “I did not leave him alone until I caused separation between him and his wife.” So he (Iblees) brings him close to him and says: “How good you are!” Those people should be reminded to fear Allaah for themselves and to stop this evil act.
Likewise, it is not the right of the father to restrict his children from their right of inheritance due to them staying in the custody of their mother. If he wrote this in his will, then that (part of the) will would be invalid and it is not permissible to fulfill it. Allaah The Exalted divided the inheritance according to His Book and He gave every rightful person his right, and then followed that by saying (what means): {These are the limits set by Allaah, and whoever obeys Allaah and His Messenger will be admitted by Him to gardens [in Paradise] under which rivers flow, abiding eternally therein; and that is the great attainment. And whoever disobeys Allaah and His Messenger and transgresses His limits – He will put him into the Fire to abide eternally therein, and he will have a humiliating punishment.} [Quran 4:13-14]. For more benefit, please refer to Fatwa 120933.
As for the custody of the children, it is the right of the mother. However, if she marries, then custody is transferred thereafter to the person entitled to it after her according to the order stated by jurists as clarified in Fatwa 84618. Some of the scholars stipulated that the right of custody for the father is conditioned upon him having a righteous female to manage that custody. This is reported by the Maaliki jurists.
If there is any dispute in such issues, it is only appropriate to refer to those specialized in looking into Muslim affairs (like Islamic courts and Islamic centers).
Allaah Knows best.