Questions on External content type and BDC sharepoint 2013

I have requirement like this:
Right now, Person A has data in excel sheet which is updated from sql server, it also has some reports in it. Data is based on a select query from 2 SQL tables. Excel sheet shows 2 cols Col1,Col2,Col3,Col4, where col1 and col2 are from SQL server and col3 and col4 are manually updated. Now they want me to find a way to migrate the data to somewhere else where more than 1 users should be able to update data.

I thought of synching the data from SQL to Sharepoint by creating external list and I created a external content type using SQL Server connection and created external list but I dont have the ability to add extra columns.

Is there any other way to do this? Please let me know

Thanks