Proposed changes to your home repair small and inexpensive.
It is necessary to supply the glass partitions (as shown in the drawings) and expanded bathroom.
The bathroom can fit a shower (bath takes up too much space. The room will be very small).
Partitions can be hidden inside the curtains and open when you need more lighting.
Furniture can be arranged in any of the options. If necessary pull-out sofas, sofa beds can be placed.
If you need a beds, you can put the beds. If you do not need a school desk, you can remove it.
In the VERSION 2 I propose to put bunk bed (if you feel comfortable).
This will add free space to the room. It can be filled with a large work desk, near to put a bookcase.