Hi @warren.harrison,
Thank you for reaching out to us!
You should be able to store data on the user’s root level, such as given_name and family_name as you mentioned, using the Management Api to update a user’s attributes.
Alternatively, you can also call the Management API through an Action as well, if this suits your needs better. Please feel free to check out the following Knowledge Article on this topic : Using the Management API in Actions .
Have a great one!
Gerald