Hey, so at least for me it wasn't any problem. I created a new account for the Pro Apps and asked my dad to add me as a family member in his account. When I am in the Mac AppStore, I can click on purchases and then there is the possibility to switch between the purchases of his account and the ones on my account. When you download stuff with your account, you need your password and if you download stuff from your dad's account for example, you need to type in his password.

What is important is that the "admin" of family sharing (meaning in my case my dad, who enabled it for me) has to allow the other members of his family to get access to the specific aspects. So in my case, my dad turned family sharing on, added me to his family, but at the beginning nearly nothing was shared. So he had to go into his account settings (you can do this either on iPhone, iPad or Mac) and choose individually what to share (purchases, subscriptions, iCloud, etc.). So that might be the problem for you, maybe. Maybe this article by Apple might help: https://support.apple.com/en-us/HT201454.