Is the husband obligated to divorce his second wife under duress and the writing of checks, and what should she do when she is pregnant by him?

Islamic law permits a man to marry more than one woman, and no one has the right to prevent him from what Allah has made lawful. If the first wife and her family object to the husband marrying another, and there was no condition in the marriage contract preventing this, then they are in error. Their threatening the husband and forcing him to sign checks for debts he does not owe is an even greater transgression. He is not religiously obliged to pay them or to divorce you because of them. The husband is advised to seek the help of wise individuals to clarify their error, and he may threaten to refer the matter to the responsible authorities if necessary. If all avenues are exhausted and your divorce becomes the solution, then you must accept it with contentment and submission. Perhaps Allah will compensate you with something better, for He says: "And if they separate [by divorce], Allah will enrich each [of them] from His abundance. And Allah is ever Encompassing and Wise."