4) Stick to the maxim “less is more” as much as you can
When the space is small, less is definitely more. The room in this image is a great example, with the bed lit up by the window. The identical individual storage units on each side leave plenty space for fun.
5) Here you see two distinct work spaces, as well as the importance of clever storage units.
6) Are renovations possible? Maybe try installing a partition, that will give each child their privacy.
As long as the light is sufficient in both ‘rooms’, this should work perfectly! Here is an example of an attic design with the bathroom in the middle.