Dynamically load categories and subcategories in wordpress

I am struggling with this for few days and can’t get a way to do it.In my wordpress admin side i created a post type called organising committee.In this post type i want to create a drop down field called committee group and according to the commitee group selected i want to display a drop down showing all of the group members dynamically.

But where can i add this committee
groups and group members.I tried many plugins but it cannot meet my requirement.Any help would be deeply appreciated.