Family sharing does not make apps purchased on iOS (in iTunes) available on OS X (Mac App Store), and vice versa.

Apps sold for iOS are available on all iOS devices linked to the original iTunes account (or Family iTune account).  

Apps sold for OS X are available on all OS X devices linked to the original Mac App Store account (or Family Mac App Store account).

If you want SkySafari to be available on both iOS and OS X then the app will have to be purchased twice, once for each OS.

If you are unhappy with the current purchase results you can contact Apple support for a complete refund, and then, if desired, re-purchase SkySafari for your preferred OS.

Thanks!