Congratuations to your son on getting in KEFW
I really wouldn't worry about not getting KECH - we were in exactly the same situation 7 years ago (missed KECH by 2 points) and worried at the time but it's turned out all for the best.
KEFW is fantastic school - many KEFW parents think it's far better than KECH (but they would say that wouldn't they
The journey is reallty not a problem - the Green Bus is a great way to make friends
Treat it as fate - he will have a great time and do well (so long as he works hard)
The size of KEFW means that there is great flexibility when it comes to 6th form - you can choose A Levels or IB - KECHB is small so won't be able to go that route.