If your format of excecl files is fixed and it do not change, then you can do the template creating process once as a site admin. After that users will not need to create templates. They can simply import the excel files as per specified templates
If not, then probably implementing a excel import solution using custom java action can do the job. You can read excel files from the java code and create required mendix objects to store data. Would be a little difficult to implement if you are not much familiar with Java.
Let’s see if others can suggest a better way