When you order date members in reversing
When you order date members in reversing order, be aware that some of the date function (example YTD, MTD) will not work as expected.
Otherwise, option I would use:
In Analysis Services Data Source View introduce calculated field with formula something like:
CONVERT(smallint, SUBSTRING(WWFieldName, 3, 2)) * (-1) AS WWeekOrderID
and then create attribute based on that field and then order WorkWeeks based on this attribute.