Currently if you have a feature layer with 3 related tables: parent -> child -> grandchild
you can join parent -> child and create a new feature layer (hosted view)
However, when you now join this new feature layer to the grandchild table you are unable to create a new feature layer (hosted view) - the option is greyed out.
So I cannot create a dashboard report that has all 3 tables updating live as the data updates. It would make sense if you can have 3 related tables that you would be able to join all 3 tables in a live view.