If you want to apply rowlevel security at a group level, You will have to perform this in the RPD at an Application role level.
Hopefully you have the Application role to groups mapping in your Weblogic Admin
Go to Manage Identity -> BI Repository -> Application Roles -> Choos eyour application role and double click -> Permissions.
Here you can set various types of conditions at a group level to achieve row level security
You can create the Group in database and map them to roles in EM ( 1:1 ) and then define your data security requirements around this application role based on dimensions or fact using session init blocks. Is that what you are trying to do ?
Refer to BISAMPLEAPP example here : Jonathan's Tech Journey: OBIEE 11g Security part 1
If you need more restrictive or additional needs then refer too :
Hope this helps,