Sounds like a good business case to completely replace the spreadsheet with a multi user, served, Filemaker solution.
You would be best served by grabbing the filemaker training series and working through it from end to end.
Welcome to the FileMaker world where your employers put you in front of FM and expect you to build software to run the business with no training.
It doesn't sound like putting the spreadsheet INTO FMP is needed...it has no data.
It sounds like you just need to use the EXPORT function from FMP to create the spreadsheet...