If a user tries to open a Workbook that is already open, then they normally get a message saying that the File is locked by a certain user and would you like to open the file in Read only mode. However, you can open a workbook in shared mode by following these steps. First open the file that you want to share, then once the workbook is open, go to the Tools menu and choose Share Workbook from the drop down menu. The Share Workbook dialog box will now appear. To enable sharing, you simply click once on the Allow Sharing check box, so that it has a tick. Once you do this other people will now be able to use your Excel workbook whilst you are working on it.
I understand how you may feel reluctant to allow an external advisor to delve into the detail of your business. I have had other clients who felt the same way. But all of my other clients found the investment they made was repaid many times over both in their business and their own work life balance. To help you we have produced a free spreadsheet which will allow you to reflect on what you would like to achieve with your business and where you are at present. If you use the spreadsheet it will help you to identify if it would be beneficial to get an external advisor or if you are proceeding in the direction you want. Once you have completed the spreadsheet we will review the results with you if you want at no cost to you.