As always providing a view on the likely sentence is not easy as we don’t have all the details. As well as that, sentencing for Causing Death by Dangerous Driving is quite complex. However, as a guide, the “seriousness” of the offence is split into three bands. When sentencing an adult (18+) offender for an offence in the lowest band the “starting point” for consideration is one of three year’s custody, with a range of 2 to 5 years. However it is likely that a judge will see this in a higher band (his is defined as “Driving that created a substantial risk of danger”. If so, the starting point is 5 years with a range of 4 to 7 years. The offence is considerably aggravated by the number of deaths caused and it would not be surprising to see a sentence near the top of that range.
However, offenders under 18 receive considerably lower sentences than their adult counterparts and a 15 year old offender could (in very broad terms) expect to be handed a sentence of no more than half the adult tariff. But as I said, it is a complex offence to sentence and there are a multitude of factors to consider.
The guidelines I mention are for a first time offender being found guilty at trial. A previous record (especially for similar offences) will see the sentence increased whilst an early guilty plea will see a one third discount applied.