As Sheila says, he has a new tool, and he's using it. Although he has his brother for company, that clearly isnt satisfying his need, and it might simply be that it's you he wants.
I'm probably not a great one to comment, as we let the boys sleep wherever they like - living room, kitchen, back bedroom, our bedroom.......
On a practical level I would go with the suggestion of placing a perspex cover on the door frame, but it wont address the emotional need which seems to have surfaced.