[kiwins]

I have to say it is a very difficult task!
I have never had such a large class and since you need to develop their oral skills which seems impossible, if there is a big difference in their knowledge, my only suggestion would be to divide them into 2 groups of similar levels and make their seating arrangements according to that (putting the higher level on one side of the classroom, and a lower level on the other). Find activities that can be done as a group and give a more difficult task to the higher level group. Use activities with short texts, maybe try "Simon says"...