Hi iFaden,
You can upload the Excel sheets to a SharePoint library which your customer can access and edit the excels.
For Excel version and approval control, you can
enable the
version control and content approval option via library versioning settings, which can record each modification and the control approval, means that modification (draft version) couldn’t be seen by others until the
modified Excel is approved by the user with administration permission.
You can also enable the Require Check Out option which allows only one user to edit the Excel at one time, there is a relevant
article.
For email sending to your customers, you can create a workflow attached on this library using SharePoint Designer, when you add a new Excel to document library,
it will trigger a workflow to send an Email to your customers with the current item URL in email body (
here ),
Or you can let each customer to subscribe Alert under Action menu in library toolbar, it will send the email alert when there are changes on library item. Or administrator
can add all needed customers from Alert Me for them per this
article.
Thanks
Regards, Daniel