Theory time!
1. It seems that Elsa and Anna's parents are Romeo and Juliet. Star crossed lovers, from two warring faction. It makes me wonder if she ran off with their father, which result in the peace between the two sides turning into a violent conflict. Or perhaps were they married as a way to bring the two sides together, and something really bad went down.
2. Okay, so I don't know if their parents are alive obviously, but I get the feeling it is only their mother who is still alive and one of the beings they will be doing battle with in this film. Which makes me wonder, how is she being manipulated? We already know they have the ability to alter memories.
3. Also while I assume the storm that ended up "killing" their parents was potentially magical now, is it perhaps that it wasn't the forest magic folk that ended up with their mother? Were the other 3 elements perhaps kidnapped, perhaps by a secret faction inside the kingdom?
4. If Elsa is the water elemental, I wonder if there is a reason she is so "ice" based. Like is this something to do with her father not being of her mother's people?
Beyond that, Olaf with the go pro and this turning into Avatar all looks great.