For the interview, draw up sample questions from each chapter and have the students practise interviewing one another or, if there are only a few students, ask them the questions yourself and give them individual feedback. In speaking assessments, remind them to keep their answers concise and focused but to give as much RELEVANT detail as they can. If they are unsure of the question, they can ask for it to be repeated and take a moment to consider their answer but they need to be aware of time - taking too long to think of an answer in an interview is not good. You could also go through different types of questiosn (interrogative, descriptive, comprehension, etc) and show them examples of the questions, discuss what type of information is required in the answer and how to best formulate an answer. Ex. Comprehension questions almost always begin with Who, What, Where, When, Why and How and require nothing more than for the respondent to extract the relevant information from the passage. Being able to identify the type of question makes it easier to provide only the relevant information.
For the writing part, give them a SIMPLE format for an essay (Intro, body and conclusion) and review topic and supporting sentences. There's not much that you can hope to accomplish with the writing if you only have three weeks BUT you can give them tips on planning an essay, structuring the basic argument and supporting their arguments. Again, emphasise that only the essential information should be mentioned and, while it's good to use the vocabulary and phrases from the textbook, these should never be forced to fit an essay or interview response.
Good luck!
