Hi Francis,
The Main Report's datasource should return all Brand and Category Names. You can use a SQL Query or report against a Table/View to get this data.
Create a group on the Brand Field in the Main Report and also create the From and To Time parameters.
Insert the Subreports in the Group Header/Footer and link the Brand Name field to the Brand Name fields in the Subreport's datasource and the Parameters to the Parameters in the Subreports.
-Abhilash