Unfortunately you can’t. If all athletes follow the same annual plan and all of them are in the same workbook you can’t. You can create different workbooks and share those. Or print the plan/calendar in PDF and share only that.
You can create Dropbox folder with PDF file, or even better use Evernote to share it. These are all low-budget variations.
I will be collaborating with one AMS company and maybe come up with something affordable for coaches. Basically making the planner in ‘cloud’ and being able to collect some data using smart phones, etc.