ISB vs BSB vs St Johns... (living in Uccle)

We're a Franco-British couple returning to Brussels this summer (and to our house in Uccle) after 5 years in Singapore. We have one last son at school who is 13. He has always been in the Belgian and French school systems but is not particularly happy or fulfilled there. He's 100% bilingual English and French. As a result we've been looking online at ISB, St Johns and BSB. ISB and St Johns have an IB average of 32 whereas BSB's IB grade average is 38!  But we live in Uccle... not Tervuren. 
- When looking at the curriculum, ISB seems more Arts based and less Science and Maths. Can anyone confirm or dispute this (Middle and High School levels)? Do any students go on to study eg engineering or medicine from there?
- A couple of families have put me off St John's saying that it is less international and that the standard is dropping. Again, I'd be interested in feedback.
- Do any BSB families actually live in Uccle?!
I'd be grateful for any feedback on these school choices.
PS I have looked at previous feeds but not found recent relevant answers.