Honestly, I think you need to accept (and help him to accept) that Cambridge medicine is really unlikely to be possible, and medicine at undergraduate may also not be possible (there's always the possibility of him doing well in a science degree and doing post grad medicine, but it is still super competitive).
That's not to say he can't try, but if those are the grades he's achieving with tutoring at GCSE (or is the only tutoring English?) it seems very unlikely that he will get the Alevel grades he needs for medicine. It's not so much about the English, as the fact that overall his grade predictions aren't great (to be clear - in a Medicine/Oxbridge context, these are great predictions in the normal world). Yes, maybe he'll pull it out the bag but the academics only get harder.
Does his school not predict 9s (I know some don't) or is it that they're genuinely not expecting him to get 9s in maths and chemistry? That (and the 7s in physics and biology) are the part that would worry me - he's going to need mainly A* at Alevel in maths/science and (to be brutal) should be finding GCSE relatively easy if that's likely.
Some kids (and particularly boys) do get into their groove late, so I'm not saying it's impossible at all but it is looking fairly unlikely unless something dramatically changes at Alevel. But I think you need to be careful - tutoring to push up his grades at GCSE may just he delaying the inevitable.
That said, I note the lap top point - are there SEN concerns? Might the issue be he doesn't really understand how to study/needs support in that area?
Sorry to be harsh and of course he can still try. It's just there is a really high chance he won't be able to achieve his dream (and this is very common for people who dream of medicine) and you now have the very difficult job of preparing him for a fall, whilst not making him think you don't believe in him.
If there's a chance it's SEN/study skills rather than ability I would focus very hard on that area though. I have a child with ADHD and specialist tutoring from someone who understands and knows how to teach him to study has made an absolutely massive difference.