Their religious beliefs are there own business. But they don’t have a right to impose them on others. If they are unable to sit next to women then they probably should consider chartering a private flight or not traveling. Their behavior was disruptive and they should have been ejected from the plane.
Make them buy two adjacent seats if they are worried about a woman sitting next to them. If that isn’t enough, they could wear some kind of clothing or headgear to keep them from seeing any woman sitting one seat over.