Does a man's divorce of his second wife count if he was forced and coerced into it by his family?

If the family's pressure to divorce the second wife is valid, then they are mistaken; because the Shari'ah (Islamic law) permitted polygyny for those who are able to be just. The divorce you pronounced is considered valid, and the pressure you were subjected to is not considered coercion in Shari'ah that would prevent the divorce from taking effect. We advise you to reconsider the second wife to avoid conflict and maintain your family's stability, and perhaps Allah will facilitate for this woman someone other than you.