Can I share Merlin Project with my family through "Share Purchases"?
So that you can test the software extensively before subscribing, we have opted for the in-app purchase option. However, in-app purchases are not shared with family members through family sharing. You can use the app licensed on the personal devices associated with your Apple ID, but not share via family sharing.
Apple explains on its support page what types of content you can share with my family using purchase sharing.