Is it possible to have two teachers supervising one room?

Yes, You can define the number of teachers needed for one duty. Just click on the supervision, from the meanu use Count and select the number. Maximum 5 teachers can be set for one supervision.

Notes
- please note, that you can specify this different counts for each duty. For example the room reguires two teachers in the morning breaks but in the afternoon only one is needed.
- this option means, that two or more teachers will be supervising same place at the same time. If you wish to specify the exact areas, it is better to create separate "classrooms".