Yep, one set of 12 Atma will give you both the Curtana and Holy Shield Atma. The books are also indeed split as the above poster stated. It is perfectly possible to do the two shield books and actually upgrade it to Animus before even touching the sword.

My big question is this: I have the Holy Shield Animus and the Curtana Atma. Once 2.28 drops, will it be possible for me to pursue the Holy Shield Novus while still working on getting the Curtana Animus? It would be awesome if we could