Judge Topolski QC has said he would not pass sentence on the two men until a Court of Appeal decision about a similar case had been heard later this summer.
However, sentencing is due to open this afternoon.
The judge earlier told the court that he was willing to offer a reduction in sentence if the defendants were to plead guilty.
He described the case as a "grave one".
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Scotland Yard said the male youths will appear in custody at Westminster Magistrates' Court on Saturday.
Windy this weekend with gales across northwestern parts of the UK. Rain spreading southeast.
Greater Manchester Police said "inquiries are ongoing to fully understand the circumstances of the incident."