Condensation and ice on Velux roof windows

We decided on Velux roof windows two years ago, and every time it gets colder outside, a lot of condensation forms on the inside of the windows. On frosty days, even frost flowers! During the day, the moisture then drips onto the wooden floor, which has already been damaged. What is wrong with the windows, and what can I do to prevent this next winter?

The windows are probably all right; the humidity in the attic seems to be quite high. What could be the cause: many plants, bathroom/shower often in use, rarely ventilated?

The relatively warm moist air condenses on the colder panes. That seems to be the building physics process that would need to be changed.