Thank you for another interesting question.
I think the first thing to sort out with your teacher students is their presence (or absence) in class. You say that they come and go because they have other classes or are busy. They should be able to let you know about this in advance. You could ask them about their planned absences and make notes about who will be in class on which day. You could put up a table in or near your classroom where these teachers can indicate if they plan to attend or not. Alternatively, is there an office or meeting room where this could be done? By doing this, you will have a better idea of who will attend and you will be able to plan your lessons more satisfactorily. Of course, there will also be people who have a last minute issue that prevents them from coming; but it should be easier for you to work in this way.
Another thing to check is whether they have chosen to work on listening and speaking or whether that has been imposed upon them. Find out exactly what they want to learn and do that with them. You might see increased attendance by doing this.
Having said this, listening and speaking seem to be the logical areas for them to work on. They probably have a good level of grammar and vocabulary. You could also work on pronunciation with them.
You can pick topics for them to study; choose a theme and work on listening, speaking and vocabulary connected to this theme. You could also ask students to give presentations on topics of interest to them. Ask them to give a presentation of 15 – 20 minutes, other members of the class can ask questions at the end of the presentation. If they are reluctant to ask questions, you can say that everybody has to ask at least one question. You can then give feedback on the language aspects and the presentation skills of the person. This will also be good practice for their work as teachers.
You can also look at the following posts in this forum: listening on 21 Sept 2004, speaking on 10 May 2004 and jigsaw listening on 18 April 2004.