Jamaat brothers' wives work in the family business with their husbands, fully clad in hijab.

Answer

Now why did you introduce the Jamaat in your question? The Jamaat does not teach violation of Hijaab. If a member of the Jamaat commits a sin, why do you attribute it to the Jamaat? If a Muslim commits murder, will it be proper to attribute it to Islam? Muslims belonging to the Jamaat, to the Khaanqas, to the Madaaris, etc., all commit sins. It is a severe malady of the nafs which prompts a person to attribute the sins of individuals to the august institutions to which they belong. You should have posed your question without introducing the Jamaat dimension. It is haraam for women to be in the business in violation of Hijaab even with the consent of their husbands. Both the husband and the wife are sinful in committing the violation.