Are the calculations worked out with table calculations?
I know you said you can't upload the workbook due to health data, but please could you create a sample dataset or redact the data and then upload the workbook?
We'll need to see how your calculations are currently being worked out.
I am not entirely sure that I have understood this completely but I have attached an idea for a potential solution. Given that this is a percent of total calculation, we cannot rely well on filtering as that (in most cases) will impact the values displayed. What you can do, however, is duplicate the sheet, select the groups you do not want to display in your legend, right click the values, and choose Hide. This will remove the value from the visualization without affecting the percent of total calculation.
You could just duplicate the chart for each group and leave a different group displayed on each one. Does this help out?
P.S. I made the workbook in Tableau Desktop 10.5. Let me know if you need it made in an earlier version.
PotentialSolution.twbx 1.3 MB