I feel for you!
( for all Tipsy & AB watchers, this is not the beginning of a beautiful relationship!!)
I don't know your son and only have an inkling that this is a sudden and unexpected deviation from your many plans.
However you know and I know, cramming can have a big downside - catastrophic loss of confidence.
If it was me, I would just be checking he knows his basic operations very well
for Maths and let the English be taken care of by talking a lot this week. Maybe learn new topics only with lots of little breaks and treats and help him to stay calm by not mentioning the word, "You've got this Wrong
It's a bit late in the day but if you get yourself organised and do it in chunks, he and you might survive the holidays.
The only other thing would be to put all your trust in his innate abilities and let him fly on his own wings.
Where are all the tutors when you need them?