Ok you are worrying about a lot of detail here but I’ll answer since you asked.
These grades on the Edin website are the minimum that he can apply with, not necessarily what he needs to get an interview or an offer. Interviews are mostly given out on his Higher results and his UCAT.
Most Scot medical schools assign applicants a score for academic performance, add UCAT ( in varying proportions ) and then give interviews to the top X percentage. Better grades mean more points.
Every applicant will have a personal statement and work experience, thats necessary for the application not sufficient to get an interview.
Edinburgh are really NOT saying “ you will have a competitive application with BBBB at English, maths , biology and chemistry from a private school” . They are just not precluding someone who has B in one of these from applying. Sometimes candidates have a disaster in one paper.
TBH if your son is struggling to get a B at Nat 5 in science and maths subjects, he is really not going to get As at higher, Bs at AH ( or 3 As for Oxford or Cambridge ) and enjoy studying medicine at uni.
So he should aim for better than AAAABBBB . Its hard to go from a B at Nat 5 to an A at higher, especially in maths and chemistry where theres a big jump.
If he’s struggling to get a good amount of As at Nat 5 he will find the workload in S5 to be even tougher. Remember that most Scot med schools wont consider resits at higher or a mix of qualifications , he needs to get the grades at one sitting.
So Im afraid that for medecine at the most competitive unis, resits are NOT an option. It’s now or nothing.
And he wont get into Oxford or Cambridge with AAAABBBB for sure.
Plus the school are saying he's capable of getting better grades .
Its not about aiming for another 3 marks to get to 70%, he need to aim for a secure A.
So for ALL these reasons, he needs to work NOW on his Nat 5 and forget UCAT and WE . That’s simply a distraction.
I dont think I said anything about 9 Nat 5s? Maybe that was someone else. Although in fact some state schools allow 8 and some candidates will do 9. But that’s irrelevant to med entry as Scot unis usually only consider the best 7.
Re oxford and Cambridge applications - the time to consider if thats an option is when he gets his higher results and UCAT score in 18 months.
He cant make a 5th medical school application anywhere in the country, the max is 4.
He cant apply to Glasgow , Edinburgh , Dundee , St Andrews and Aberdeen - thats 5. Let alone another English one on top.
However as I said before, I think UCAT and UCAS is a distraction for you and your son right now. He just needs to work on his Nat 5s as the school has advised, get his best possible grades ( not what he reckons is the bare minimum ) and keep his options open.
I hope you enjoy your holiday and manage to get a flat and legal advice sorted out.