Hello Ekaterina, In our school we use skype for videoconferencing. We have a computer that is connected to an interactive whiteboard in the library. The students sit around on chairs and watch the conference on the board. If three different users or more are in skype, you cannot use the video, it just becomes chat. So we have one computer, one microphone and one small webcamera and use them to talk to, hear and see you, but your image is projected via a data projector onto the whiteboard or wall.
So, it will be just the same as you using it with one student, except the class becomes the 'one student'. Does that make sense? So, if you have a webcam on a mac, that is fine, but you will need to try and project that onto a wall or board, so that all your students can see at once. Keep in touch and let me know when you are ready to try. I am happy to just try with you first and no students, and then bring the students in the next time. Hope you can understand me.