As far as I've ever heard iggy's are not nocturnal but that doesn't mean they won't move at night to nibble on food, poop or just find a new, more comfortable perch. Are your two iguana's in the same cage?
When I purchased them they were in a 20 gallon together cramed in there. Now they are in a big crate but are together. This is only for the time being because Nancy is going to a new home with my friend who is more experianced with Iggys. I am keeping Sid though and building an enclosure. When I say up at night I mean they are like wide awake. Walking around and all that.
Not sure, however, they are not meant to be housed together so likely if they are acting out of the norm for iggy's it's due to stress and one trying to dominate the other for night perches, etc.