How to do subgroups for forum categories


I have a portal for participants, which is built on Wordpress (theme Pacific).

The portal represents areas with materials + forum area.

I use membership plugin to grant the access to the portal for participants.

I have a number forum categories which I want to put in special order under a particular subgroup (separate header). Below is the visual on a forum page (now I just have the list with Category 1, Category 2, Category 3, etc)

So it looks like:
Header; Admin
Category 1
Category 2
etc (in each category each participant can create a new topic)

Header: Home work
Category 1
Category 2

My progremmer can't figure out how to do it. He said that we can use some plugin (he doesn't know which), different theme (not sure) or to do it somehow custim made (but I don't like it if I whant to change smeting + a lotof work involved)

Could you advice me on easier option - plugin to be used or something else? May be you havesomething in Memebership?