What is the ruling of Islamic law regarding my divorce due to accusations of witchcraft and the instillation of doubt, and is divorcing for the sake of the first wife's harm the solution to that harm?

Accusing a wife of sorcery without proof is an injustice and abuse. As for divorcing her, if there is a need for it, it is permissible. If there is no need, it is disliked (makrooh). Some scholars may even consider it forbidden, based on the Prophet’s (peace be upon him) saying, "There should be no harm nor reciprocal harm," and because it harms both spouses and destroys their mutual benefit. A man divorcing his second wife to protect his children from ruin is neither unjust nor forbidden. Divorce can sometimes be good, as Allah Almighty says: "But if they separate [by divorce], Allah will enrich each of them from His abundance."