I would suggest your DS (with your help) contact a few admissions tutors at the kind of calibre of university your DS is aiming for and ask if they could advise informally (stress informally, as often admissions tutors won't give formal advice on issues that are not completely clear cut and will just give a standard blurb or refer you to existing publicly available generic guidance) about a) how they would view the breadth of his GCSEs if he drops both RE and geography given the other subjects he is taking, and b) how would they view him (also) dropping English lit. This would help him in his decision about where to focus his attention and is also information he can show to the school. I suggest contacting a few admissions tutors because practice across universities will vary, particularly when you add in his recognised processing difficulties.
To give you an example, at the university where I work, if he dropped all three of RE, geography and English lit, he would have a just about acceptable but not very strong GCSE profile, particularly in context if everyone in his school is also taking many GCSEs.
Our formal guidance specifically states that we do not require applicants to have completed the EBacc, but this is accompanied by a much vaguer statement about expecting applicants to have "a range of subjects" with good grades at GCSE and to demonstrate "a broad general education" and elsewhere we say that we consider "your overall subject profile". How an admission tutor would interpret 'a range of subjects' or a 'broad general education' is open to question and he is missing not only a humanity/social science but also an MFL, so if he dropped RE, geography and English lit, he would basically just be offering maths, sciences and creative arts with what we would consider "good grades" (and one English with a not so good grade).
There is also a question about how much credit he would be given for his large number of GCSEs. In my own department, we are not keen on statistics when taken alongside maths (and further maths) or engineering when taken alongside physics. Having multiple instances of these kinds of substantially overlapping subjects is less of an issue at GCSE than it is at A Level (where we specifically state that this is undesirable and would generally exclude one of the overlapping subjects from offers), but we also wouldn't give as much credit for them as we would for non-overlapping subjects as we don't view them as requiring a similar level of work or as demonstrating a diverse range of skills (in my subject we review holistically and don't formally score, so you gain little from having your total number of GCSEs inflated by subjects we have an issue with). So we wouldn't be looking at his GCSE profile and thinking 'well he's still got lots more GCSEs than average' because in our eyes he doesn't really - if he drops all three of RE, geography and English lit, he has the rough equivalent of 8 or 9 GCSEs, which is low-ish average in our applicant cohort.
For CS we would only require a 4 in GCSE English Language, so his grade would be low but fine.
However, at other universities ranked much the same as us, e.g., Imperial, he would just be a straight 'no' because they require a minimum of a 6 in English language as part of their basic entry requirements. On the other hand, Imperial would probably have less concerns about his GCSE subject profile and emphasise that they want to see an interest in maths and science. His large number of GCSEs would be a plus at any university that uses an algorithm just based on total number of GCSEs.
For me the priority would be getting his English language grade up as a 4 is going to limit his university choices the most and a 5 will still rule out some of them and, barring some leniency for his documented processing difficulties, would exclude him from several universities that should otherwise be within his reach. The breadth question is at least open to a bit more interpretation and would only be a little improved by keeping subjects just to offer a more diverse range when his grades in them wouldn't meet the threshold to be considered "good" by the universities he might be interested in attending.