You are spot on when you say that students pick up their mother tongue by listening. This is the same way the English Language also needs to be learnt.

You need to create an ambience within the class, where students come to a level where they take the initiative to come out and speak, without you initiating it. They should be groomed in such a way, that mistakes or grammaticasl errors should not be pointed out and your focus should be purely to make them speak in English mandatorily.

Also ensure that no one is allowed to use their mother tongue in the classroom. You need to be ruthless on this. Gradually when you enter the second phase of training, you need to tell them, that we speak our mother tongue unconsciously. In the case of the English Language, to get the ideal rate of speech, right pronunciation and strucutures, they need to speak consciously.