Hello Akasnoopy,
Thanks for replying with this information!
I’m sorry if I misunderstood the situation to begin with, but I understand now that Touch ID is working everywhere, including the iTunes & App Stores, with the exception of being able to approve purchases from Family Sharing.
In this situation it may be necessary to contact Apple Support directly. Contacting us will allow us to dig in to the situation and help you resolve this situation as quick as possible. Please use the attached link to get started.
Apple - Support - Topic Selection
As always, please reply and share any information or steps you worked through to get this resolved. Thanks for being part of the Apple Support Communities and we look forward to your continued involvement. :D
Have a great day!