I haven't worked much on this but I belive your order statement is wrong. It should something like following-
WITH XMLNAMESPACES('http://mch.com/IF002/SD/mch/I_mch' as ns0)
INSERT #BrandData
SELECT
Data.value('(nickname/text())[1]','VARCHAR(100)') AS nickname,
Data.value('(username/text())[1]','VARCHAR(100)') AS username,
Data.value('(IsActive/text())[1]','VARCHAR(4)') AS IsActive
FROM
@xmldoc.nodes('//ns0:mch_In/Data')AS BrandData (Data)
Please try and let me know if you still have issues. :)