I would say for the story, don't learn a story or script, it's okay to have a few descriptions for the weather or some things about facial description, but if you repeat the same general plot line, you aren't completing the task (costing AO1 marks) because you won't be reacting to the picture and the quote/prompt given to you, scripts are not recommended by the exam boards and they emphasise this every year. Many on SM etc share story ideas, the exam boards don't like this and also can always tell, learning a few phrases or things you might want to say (as in vocab) about the weather, or clothes or facial descriptions etc is fine, but you need to be adapting and reacting to the content of the prompt and picture.
The best practice for this question is just that, exam pratice, looking and finding pratice questions and giving yourself five minutes to plan and go from there, do a few full out (timing and the whole length and get teacher to mark), but also writing a paragraph or planning detailed points is also useful. Then reading is key, the kids who read have more breath of language, ideas, are more aware of nuanced techniques and how to create coherent flow - get him reading more OP, not diary of the wimpy kid, it doesn't have to be old books, they're are lots of modern texts which he can read. Look at the women's prize for fiction, the prize for fiction in general, Lit in Colour texts which they recommend etc, that will benefit him a lot.
If the tutor seems good, get him to try it, both English Literature and Language are highly valued GCSEs and whilst he may only need a 4, if he can push for higher he should, he never knows when it can be helpful. Even aside from the grade, the skills of English will always be needed, the analysis, nuance, comprehension, forming arguments etc. He may hate it because of his experience in class and also the fact he's not doing well, sometimes with a better 1-1 time, development can increase your joy in a subject.
I'd also say for Lit, it's getting to know the texts inside out, essay plans are the best - scaffold around a past papers question and make a perfect version perhaps on Google docs etc, let that contain everything on structure, language, the specific character, link to themes, context, your thesis (should run across your essay). Then you should focus on learning those points, creating your own ideas as well - not just the generic points everyone will have, have some nuance, have specific ideas, make sure you develop them and develop your 'writers voice', this comes with practing as much as possible. Try and abandon set sentence/paragraph structures, which just repeat over and over with no actual depth of analysis as well, PEEL is quite basic, and whilst it's right about some of the things to include, you don't want it to sound very prescriptive, the more you write, the easier it is to get away from that and develop your coherence without any structures, you'll still hit all, if not more of the same baseline requirements, but it will sound more coherent, have a strong idea and thesis running through, show a deeper analysis of themes across the book etc and tying in context and quotes where needed.
You don't say if he's in Y10 or Y11, which one? Even so I'd say that at the start of Y11, I was at a 5 in English Lit, and my essays flucated around that, anyways worked my arse off, and only lost 4 marks for the total GCSE in the end. So if he's diligent, works well with his tutor, reads more, practices questions (make sure his teachers mark these, they don't mind if you put the work in, they want you to do well), he can progress a lot, it's easier to jump between lower grades as it tends to be bigger picture stuff which they need to change, and if they're consistent, they can make lots of progress and enjoyment can grow sometimes as well. I'd get the tutor and see how it goes, help him to not see himself as useless or just not capable of getting better.