What is your advice to my husband, what is the legal ruling on him divorcing me to please his wife, and does he sin by doing so?

It is not permissible for a wife to demand the divorce of her co-wife. Satisfying the first wife by divorcing the second is considered highly reprehensible (makrooh jiddan), and it may even reach the level of prohibition (tahreem), especially if matters are upright between the husband and the second wife. The husband must strive for reconciliation and harmony between his two wives, and he should not demolish an existing family to please another. Furthermore, the family should intervene to advise the first wife that her demand contravenes Islamic law (Sharia) and that she should love for her sister what she loves for herself.