One point that comes up over and over is to cut drinks out before a certain time/before bed and ensure he's drinking enough during the day.
The reason for this is that the bladder needs to recognise what full feels like before voiding. Sometimes children are so busy enjoying the day they are drinking a few sips of a cup and never finishing a whole drink in one go so are dehydrated during the day which adds to bed wetting.
Suggestion:
Wee as soon as he wakes.
Drink one whole drink by his bed on his return.
Breakfast with another drink.
Drink at about eleven with snack.
Lunch with a drink.
Drink at about three with another snack
Drink with dinner
Last drink at about 5/6pm.
Wee before bed.
Initially watch him drink the whole cup of fluid to ensure he's drinking it all and not leaving most of it. Drinks should not be fizzy or caffeinated.
20 minutes after a drink, ask him if he needs a wee but don't encourage him to have a try. After a bit of trial and error you can help him learn what a full bladder feels like.
He should not wear nappies/dry nights etc during this time.
You might want to wake him at about midnight/before you go to bed to see if he needs another wee but try to phase this out over a week. Once he has this under his belt, his body should recognize the feeling of a full bladder which should wake him even in a deep sleep.
Being on a Christmas holiday with family backing this sort of plan could be a great chance to get him dry at night.
If it doesn't work, then a GP to investigate if it's actually a medical problem.