Is there a reason that everyone can't respond to a single Form? Why do your users need to publish their own Form?
If you did that, you wouldn't need Flow as Forms natively exports to Excel.
As long as all of your users have access to the Excel workbook, technically there is no reason why all of the Flows can't be writing back to the same Excel file. You could add a column to indicate the form that generated the new row of data.
I suggest that a better way might be to have all of the Flows write back to a SharePoint list rather than an Excel workbook. You can, at any time, export he SharePoint data to Excel. I woiuld rather use SharePoint than Excel because I suspect that it is likely that you'll run into file locking issues if you use Excel.