Trending @HCL; Need suggestion

I am working on 24/5 support project , 5 members in my team, we have a roaster plan for every 2 weeks with night shifts and 2 womens are obeying night shift as mentioning infant and health reasons, remaining 3 members getting night shift very frequently, if one person will get any health issue that impacting others health indirectly as foing extra night shift, informed to manager as well but manager baised to 2 persons whom are not taking night shifts that significantly visible. What would we do for getting proper frequent between night shifts.