How to share Family calendar with non-family member?
You can share a Calendar with anyone in your contacts list…

Right click the calendar in the list on the left > Sharing Settings…

Start to type the name &amp; select from matching contacts 

As I recall [it's been a long time since I set mine up], they must have an iCloud account to be able to actually use it, so you'd add their mac.com, me.com or iCloud.com address.