The latest convictions come as talks between Khartoum and the rebels falter.
JEM rejected Qatar's efforts to broker peace talks with the Sudanese government in April.
A spokesman for the rebel movement cited the Sudanese government's expulsion of 13 foreign relief organisations from Darfur last month, and the death sentences against its members, as reasons why peace talks could not continue.
The United Nations says that 2.7 million people have been forced to flee their homes and up to 300,000 have been killed since ethnic minority rebels began challenging the Arab-dominated Khartoum regime in early 2003.
Khartoum says that only 10,000 have been killed.