Can I classify users of the same group into 2 different categories?

Hi to all.

I have defined 6 groups of users in my Admin console.
In my process scenario, I have 2 different categories (roles) of users (representatives & administrators).
Does anyone know please if I can classify (divide) users of the same group into 2 different categories?
I ask this because in each one of my 6 groups, some users are representatives and some others are administrators and I want to make the assignment of tasks based on their role.

Thank you in advance,
Steve