They were among seven people who appeared at Derby Crown Court on Friday.
All denied committing the alleged offence between 1st June, 2010 and 31st May, 2011.
The four from Retford are Jonathan Ellis, 22, of Oakdale Road, Benjamin Kirk, 36, of Union Street, Ashley Lambie, 26, of Kingsmead and Peter Lawrence, 21, of Coates Close.
Bail was extended and they were ordered not to change mobile phone numbers.
A trial is due to start on 12th September and could last for six weeks.
A second trial has been provisionally fixed for 26th November.
The other defendants come from Newark, Doncaster, Middlesbrough and Chadderton, near Manchester.