This is a very common problem at the moment. On the wooden windows The condensate is even penitrating the joins in the window. This is causing the timbers to spread. This inturn is damaging the handles, which inturn damages the handles and locks (espags), in that order.
The only answer is ventilation ventilation ventilation ventilation.
Where ever possible, even in this weather, open the windows periodicly, during the day.
To prevent the mould / fungus / and staining, go to a specialised paint store, eg, crown or johnstones (spell) and get a perventitive paint.
As a side, put wd40 on the hinges.