There is no limitations to how many students can attend one online lesson. Of course the tutor who is conducting the lesson must have enough bandwidth to accommodate the number of students he or she wants to allow in his or her class.
Though the more students are in one classroom the more server processing power and server time will be used which will mean higher server cost, but Wiztut policy is to allow reasonable size group lessons for all of our tutors. It is a good teaching and pedagogic practice to keep your the number of students attending an online lesson to five or less.
Our experience is that it is not very practical to hold lessons where more that five students are attending. An online lesson by the virtue of being online, are more difficult to control that face to face classrooms. Hence to guarantee that lessons are productive it is important to limit the number of attendees to 5 students.