Please try "add to context" for the two filters.
Yep i tried its working! thank you for the response.
I created a second dashboard in your workbook and tried it myself.
1) I added both the worksheets to the dashboard and made them appear/dissapear by using the parameter
2) I added the filter category & sub category to both the worksheets
3) I added the 2 filters to the dashboard and applied them to both worksheets
Now the filters are always visible and they work on both the units & sales.
In case you have any more question, please don't hesitate to respond.
You can find the workbook attached, I did edit it with version 9.3. I hope that's not a problem.