Without knowing the structure of your hierarchy it's difficult, but at a guess I'd say that your query is doing exactly what you are asking it to - showing descendants of level 13. If this is the last level in the hierarchy then that would be itself. Try using your lowest level in the hierarchy instead.

Your problem is then that due to the descendants function you'll be bringing through values for Employee ID and Grp from each existing level below the hierarchy you are looking at. I would suggest the approach of making these values member properties. Have a look at the Employee hierarchy on the AdventureWorks cube to get an idea of how this is done. Then your query could look like this (example against adventureworks):

WITH MEMBER Login AS

[Employee].[Employees].Properties( "Login ID" )

MEMBER Email AS

[Employee].[Employees].Properties( "Email Address" )

SELECT

{Login,

Email,

[Measures].[Reseller Sales Amount]} ON 0,

DESCENDANTS([Employee].[Employees].[Employee Level 02])

ON 1

FROM

[Adventure Works]

Apologies if this isn't what you are looking to ultimately achieve....