The anodize process, properly done, is not the root cause of the cracks. Without seeing or inspecting the failures up close, most likely it is a failure from fatigue /cyclic stress, a stress riser from a notch or cross section change, or overloaded area.
I would wait and see the response.
As for the best material, it will depend on who you ask and what priorities they place on their tandem adventures.
PK