It's hard to compare Scottish qualifications.
The kids here take three lots of exams over three years.
National 5s which are GCSE standard but taken at age 15. Our (state) school only offers 6 subjects so there are fewer subjects to revise which must make them easier to get a good mark.
My son achieved 6As in these exams. N.B there are no A stars awarded in Scotland so the highest grade is an A.
Highers are taken at age 16/17 and a A grade is 33 UCAS points so they are considered harder than AS levels.
My son achieved 5As and a B at Higher which is how he obtained an unconditional offer from Edinburgh, as they base their admissions decisions mostly on Highers. There are only approx 4,500 students in Scotland who achieve 5As at Higher in the same year, so it's probably considered the same as 3A stars in the RUK.
For Law at Oxbridge, Oxford require AAB at Advanced Higher which in UCAS points is the same as two A stars and an A, whereas Cambridge require AAA which is identical in UCAS points to three A stars.
HOWEVER, to achieve an A grade you only need 70% overall in the exam. The Advanced Higher exams are considered more difficult than A level, partly because you take them over just a year. Many students don't take Advanced Highers as they are comparable in difficulty to the first year of Uni in Scotland. This means, however, to attain an A grade, you need to be in the top 24% of your cohort (although only the most able students go on to Advanced Highers).
Sorry about the essay, but I hope this helps explain things.