who all were the accused on trial?
John and Christopher Wright, Robert and Thomas Wintour, Thomas Percy, Guy Fawkes, Robert Keyes, Thomas Bates, John Grant, Ambrose Rookwood, Sir Everard Digby and Francis Tresham.
Gunpowder Plot
His fellow plotters were John and Christopher Wright, Robert and Thomas Wintour, Thomas Percy, Guy Fawkes, Robert Keyes, Thomas Bates, John Grant, Ambrose Rookwood, Sir Everard Digby and Francis Tresham. 
who was king at the time of the gunpowder plot King James I what was this plot? It was a failed assassination attempt against King James I by a group of provincial English Catholics why did they want to kill him? So that they can install Elizabeth on the English throne as a titular Queen.
wiki:7702517
Gunpowder Plot [SEP] Introduction
His fellow plotters were John and Christopher Wright, Robert and Thomas Wintour, Thomas Percy, Guy Fawkes, Robert Keyes, Thomas Bates, John Grant, Ambrose Rookwood, Sir Everard Digby and Francis Tresham. Fawkes, who had 10 years of military experience fighting in the Spanish Netherlands in the failed suppression of the Dutch Revolt, was given charge of the explosives. The plot was revealed to the authorities in an anonymous letter sent to William Parker, 4th Baron Monteagle, on 26 October 1605. During a search of the House of Lords in the evening on 4 November 1605, Fawkes was discovered guarding 36 barrels of gunpowder—enough to reduce the House of Lords to rubble—and arrested.