Op I have been thinking today about you and your ds, here are some thoughts:
He won't be doing combined lit and Lang GCSE as there is no such thing. Perhaps the school has combined the two subjects for a yr 10 mock as they have only covered one set text.
This helps yr ds as if he is a good writer (creatively) then he may do better in Eng Lang. Look at the spec but he has to write two pieces of free writing.
If he passes Eng Lang then Eng lit doesn't matter - as in, college, apprenticeship, future job is going to want one of the two at grade 4 or above.
If he really wants to do well at Eng lit, he is going to have to read the set texts. Doesn't matter how many quotes you learn 🙄 if you've not read the book you will struggle. The theme of Scrooge's fear in ACC is not that obscure. Maybe it's not in the revision guide, but if he looked at that without reading the text, sorry but he's going about it the wrong way round.
What examiners want to see is knowledge of the text. What happens when, why, what effect does it have on the reader - not telling the story, but if you have read ACC (it's pretty short) you will know that Scrooge is afraid of the ghosts, of his death, of no one caring about him; earlier he is afraid of spending money, when young he is afraid to enjoy life, and so on. This question won't come up next year tho. But if he won't read the book, Eng lit is going to be tough. Sorry to be harsh, blue eyes me I sympathise with you and your son as it won't be easy.
I would talk to him about what he plans to do next year and go from there.