Is it permissible to compensate the second wife with a monthly sum to bring her standard of living closer to that of the first wife, especially since she has dedicated herself to raising the children while the first wife receives a retirement pension? And what is the legitimate Islamic solution for this issue?

A husband must be just between his two wives in terms of spending, clothing, and lodging; otherwise, he is sinful, for the Prophet, peace and blessings be upon him, said: "Whoever has two wives and inclines to one more than the other will come on the Day of Resurrection with one of his sides drooping." It is permissible for the husband to allocate to one of his wives additional money beyond what is obligatory, as long as he has fulfilled his obligations towards the other.