I think the GCE A Level 5A* or 6A* is already a remarkable outstanding profile. All of them studied top ranking independent boarding schools.
I have no idea on the conversion arrangement but one of them gave up the offer of Medicine from Cambridge and is studying medicine programme in HK now.
Not sure how much easier it is to get into medical schools in the UK as each medical school only has a quota of ~7% of its places reserved for international students, so still very competitive!
Agree that it is not easy to get into medical programs in the UK as Medicine and Law are typically the most demanding majors in the UK universities as far as admission requirements are concerned. But with over 60 medical programs available (according to ucas), a lot of them are bound to be easier to get into than the HK ones.
You can only study law or medicine at graduate level in the states. They are also not making it easy for you to come back to practice law or medicine in Hong Kong.