Create an "Edit Only" share feature separate from "Edit and Share" or "Admin" share role
The way it is set up now, when you give someone edit access, they can then share the spreadsheet with others as if they are the admin. There should be more sharing access right roles like google. Edit Only should not allow someone share with other, but you should be able to create a spreadsheet or document that you can give someone Edit and Share right to or Admin rights to. Then those admins should be able to add people but they should never be able to delete the owner off. The owner should have right to reassign ownership of the sheet too (like google) for situations of turnover, reassignment of functions and duties, etc.