Damp in cupboard understairs and landing

[stridesy]

Hi there is slight damp patches in the landing. Just slightly round the window and a few patches on the wall. Not a huge issue. The landing window does not open.
Under the stairs I noticed our coats going mouldy. I was thinking to clear out and repaint and then I can leave the door open more to air but any advice on what I can do?
Also I was wondering if I painted the external wall with damp proof paint if that would help?

paint will not repair the fault that is causing excess water in your home.

Does anybody drape wet washing inside the house?

Post some photos of the damp patches please. Include your hand or something to show scale, then stand back and show the entire wall, floor to ceiling. Also photograph the outside of this same wall when it's light; showing ground to roof.