What is the ruling of Islamic law on living with a man who has a disbelieving, sorcerous wife, and he knows this, and he is considering aborting the fetus, and what should the wife do?

Accusing a Muslim of disbelief (kufr) or of sorcery without clear proof is a grave and forbidden matter.

And even if it were assumed that your husband's other wife is a sorceress, it is not forbidden for you to remain married to him. He is not permitted to ask you to abort the pregnancy, and you are not obligated to obey him in that. It is forbidden for you to have an abortion if it is legislatively prohibited.

Your husband must treat you with kindness and deal justly between you and his other wife. It is not permissible for him to favor one of you over the other unless the one who foregoes her right does so willingly.