Your duty is
to provide for your wives, children, mother, and sister on a reasonable basis, that is, to meet their needs as much as you can. Moreover, it is not permissible for you to save money for any of your children to the exclusion of the others. However, it is not necessary to pay the same amount of Mahr to both your wives. May Allah guide to what He likes and pleases Him.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.