Liam Smith, George Cowie and Blair Thomson, all 17, took off with sports cars from outside the mansion of oil tycoon Sean Dreelan in July last year.
Cowie and Thomson broke into the Banchory Devenick property and stole car keys - despite being too young to drive at the time.
The trio then drove away the vehicles the night.
All of the stolen vehicles were recovered and police eventually traced the trio, who all lived in Aberdeen.
Yesterday Smith was told by the sheriff to expect a jail term for his part in the thefts when the case called at Aberdeen Sheriff Court.
Sheriff Graeme Napier called for reports on all three teenagers yesterday and deferred sentencing until next month.