Will he be charged

[Whatmonth]

Our grandson 18 was driving with 3 mates.
He was driving down an unfamiliar road.
Came down a hill and there is a very sharp bend with a stop junction.
The sign to give way is behind the corner and a lamppost.
No other car was involved. His car went into a wall.
At the scene he was arrested as the lads in the back were hurt.
Released without charge or bail. Waiting for any reports to come back.
One badly bruised, the other had a couple of broken ribs.
DGS was tested for drink and drugs both negative.
(Waited 4 months for the results of drugs)
Police have confirmed he wasn't speeding.
No problem with his car.
Insurance company are saying they class it as an accident.
They agree the stop and give way sign are in the wrong place.
The police officer is going to discuss the case with his chief officer
which could take a few days.
In this situation does anyone know whether he will get a caution, fine, points or what.

In reality it could be any of those.

Best case outcome is that he could be given a talking to by a police officer and be sent on one of those courses aimed at young (mostly male) drivers that aim to shock them into not becoming one of the tragic cases where they kill themselves and a car full of their mates by crashing into a wall or similar.

I know the signage may not have been helpful, but it's likely that lack of attention or experience was also a contributing factor.

His job is driving so he is careful. And the 4 of them are into fitness so don't drink.
This took place in a town 30 miles away they had gone to see a sport event.
It is a bad corner which even an experienced driver if unfamiliar would have a problem. (Son and Dil have taken photos of the area)
My Dil has found out that there is a petition to move the signs.

Reposting in legal would get you more helpful responses.
He shouldn't accept a caution if he hasn't committed a crime.
The CPS will only take forward a case with a realistic prospect of conviction. I assume the charges you are worried about are dangerous driving or careless driving - does his solicitor think he was driving badly enough for either of these to be made out?