"It is better to have scars from having tried, than to be intact from never having tried"

Love this, I'm so passionate about promoting creative writing!! I think it's important to separate classes which focus on creative writing from classes which aim to correct a students' grammar etc. Of course there will be some overlap, but it definitely can have a negative impact on creativity if the correction of creative writing pieces becomes a grammatical exercise. I think the role of a creative writing teacher is a very difficult one- the best kind of creative writing class is always dialogical, which is difficult to truly achieve in a one-to-one scenario. I would actually suggest you get him to submit your students' work to writing communities (perhaps Reddit has a subreddit?) willing to give him feedback, and then help them sort through and comprehend that feedback, giving pointers on how they could modify their work from that feedback. There are also certain exercises one can do to edit themselves, but in the end, that edit must come from their genuine belief that it is an improvement on their first draft. One of those exercises is free-writing something, selecting what they feel is the most important sentence from that writing, placing it at the front and then editing their work from there. You might want to look into the process writing model as well- working for extended periods of time on the same piece and modifying it via feedback before moving on to another. Of course, this achieves a different goal than doing different creative exercises every lesson. Also, writing is almost never improved in isolation- reading extensively is almost always a must for anyone looking to improve, unless they are natural genuises (odds are usually that they are not lol). Ultimately, I view our role as guides. You are not "correcting" their content- you're helping them send the message they want to send in the most effective way. There is always room to improve and that's not a bad thing- every famous writer has obsessively drafted and re-drafted their work.

You should definitely wait for a native speaker to answer, so I'm just leaving my two cents as a comment! In my personal experience, I've only used the first three to mean "why". "Warum" and "wieso" are I think basically the same (I realised my German friends use "warum", Swiss friends use "wieso"). "Weshalb" also seems to me to be a synonym for the first two, but less common. I personally use "darum" only to ANSWER "Warum?" or to mean something like "of that". It's in the same "type" of word for me as darauf, daran, etc. I've never used it as "why". I think sometimes you can use it in a similar way to "deshalb" and "deswegen" but I'm not sure. "Deshalb" to me clearly means "therefore", as in "I am sick, therefore I couldn't go to school". Also never used it as "why". I use "deswegen" when I want to say "that's why", as in "He was lazy, and that's why his business failed". Actually it's kinda like deshalb? But I have no idea how native speakers make the distinction.