Reporting Requirement

Hello I need some help with reporting requirement -

There are two seperate parent nodes -

Parent ABC

Parent XYZ

ABC has 3 base members - A_1,B_1,C_1

XYZ has 3 base members - X_10,Y_10, Z_10

Now my report requirement is that the client wants to see sum of all the basemembers of ABC and XYZ parent nodes except account A_1 & X_10 in a cell. Keep in mind that this has to be done using one eVDRE. And also keep in mind that there could be more base members later on in the future, so I cant just do B_1 + C_1 + Y_10+ Z_10.

Please advise on the approach.

Thanks.