It's really very hard to teach so many students. I find it impossible... Anyway, if you have to teach them,you should try to it in groups. Let's say you can have 5 teams, seven students in each... Write the task on the blackboard, let them discuss it inside their teams and then they can discuss it together. It's much easier to teach grammar. you explain the grammar material first and then they are given tests. I hope I helped you. Cheers!