A couple of questions. Are you employed by a company, a freelancer, or a business owner? I note you mention “co-workers”.
If employed by a company, I think they would and should supply Office 365 for your work computer. Or are they such a small company that they do not have the resources or an IT department and expect employees to provide their own computer and software?
Keep in mind that there are risks in sharing files - sending and receiving files if there are not good virus protections in place on both ends. And FWIW, I’m not a big fan of using a personal computer for work as an employee. Your personal computer and files IMO should be separate from your work computer if employed by a company.
While technically Office 365 Family is licensed for personal use, if you are a freelancer who shares spreadsheets with others, it’s doubtful Microsoft is going to “raid” you and send you to a gulag. Not to say they couldn’t but from my understanding they are more concerned with larger commercial businesses who circumvent licensing agreements to install copies on more computers (seats) than they are paying for or are using pirated copies.
If you are a business owner managing your employees’ computers and software on a network, you would want Office 365 Business because of the enhanced security and management tools. But that doesn’t sound like your case.
But if you are thinking of purchasing Office 365 Family for 6 devices and sharing that with “co-workers” and or employees of your business or the business you work for, this would likely be violation of the licensing agreement. Don’t recommend.
There is also the question of whether you are just sending “co-workers” spreadsheets or want open collaboration, i.e. allow others to update a shared spreadsheet in real time via MS Teams or One Drive on a shared network. If you need that type of collaboration, you need Office 365 as it, unlike Open Source or Libre, is in the “Cloud”.
Also, it depends on the complexity of your spreadsheets. If your spreadsheets are relatively simple, other than the hassle of saving or opening using the correct file extension, you should be fine. But if your spreadsheets are more complex, you could run into issues as not all features in Excel are supported in Open Source and you could lose some formatting and functionality.
Differences between the OpenDocument Spreadsheet (.ods) format and the Excel for Windows (.xlsx) format
https://support.microsoft.com/en-us/office/differences-between-the-opendocument-spreadsheet-ods-format-and-the-excel-for-windows-xlsx-format-3db958c8-e0ac-49a5-9965-2c2f8afbd960
Microsoft 365 Family vs Microsoft 365 Business: which is better for work?
https://www.techradar.com/features/microsoft-365-family-vs-microsoft-365-business
What’s the difference between Microsoft 365 plans for home or business?
https://support.microsoft.com/en-us/office/what-s-the-difference-between-microsoft-365-plans-for-home-or-business-31c36a5d-a13d-4b7d-9b1f-2076accbeeab
thank you for a most thorough reply
much appreciated