In case of In-App Purchasing, it doesn't allow family members to share it.

For most people purchasing subscription licenses in our app after having used the trial version of Nine, they want to share the purchased app's license with their family. But it's impossible for users to purchase an app through In-App purchasing. This is the exception of Apple's license policy related to In-App purchasing. If you want to purchase Nine app license without Apple market's policy restriction, you have to contact our sales team before purchasing it. 

In principle, unfortunately, we don't have any right to transfer the license. We fully understand your desire to use your family's email accounts as one license for Nine app. By means of Apple policy, if you purchase an app through In-App Purchase, it doesn't allow your family members to share it. It's Apple's sales policy, not our one.

In addition, in case that you share with your family using purchase sharing, In-App purchase is excluded from this case. Therefore, it's come under this clause in case of you. Please see the link below. Go to the "What you can't share section" in the document below.

https://support.apple.com/en-us/HT203046

Family Sharing is enforced so we cannot turn it off.
https://stackoverflow.com/questions/26213420/how-to-turn-off-family-sharing-for-an-app

You cannot transfer from one account to another, except if you set them up as part of Family Sharing".
https://apple.stackexchange.com/questions/197228/transferring-apple-id-purchases-to-another-apple-id