What is the ruling on obeying a husband who prevents his wife from visiting her parents with her children, and who discriminates among the children in this regard, and is it permissible for the wife to treat her husband's family in kind?

Maintaining kinship ties is obligatory, and severing them is forbidden. Therefore, it is impermissible for a husband to prevent his children from visiting their grandparents without a valid reason; this would be an injustice to your parents. Try to resolve the disputes between your husband and your family, and remind him, for the sake of Allah, that preventing his parents from seeing their grandchildren is an injustice. Otherwise, seek the mediation of righteous people. If he does not comply, you may enable your parents to see your children without his knowledge, unless you fear divorce. In that case, obedience to him takes precedence to preserve the family. The husband has a greater right to obedience than the parents, for the Messenger of Allah, peace and blessings be upon him, said: "Had I been commanded to order anyone to prostrate to anyone, I would have commanded the wife to prostrate to her husband." Do not prevent your children from visiting your husband's family in retaliation for his treatment of your family, for every action carries responsibility before Allah.