Short answers, pulled from the story.
Emperor Alexander I died on the 1st of December 1825, triggering a constitutional crisis that paralyzed the Russian Empire. His death created a dangerous vacuum of authority because his brother Grand Duke Konstantin Pavlovich had privately renounced his claim to the throne two years earlier without public knowledge.
On the morning of December 26 approximately 3,000 men assembled in Senate Square refusing to swear allegiance to Nicholas I. The standoff ended when three artillery pieces opened fire with grapeshot ammunition scattering the rebels completely while many sank into the freezing Neva River as ice broke under bombardment.
The Supreme Criminal Court sentenced five rebels from the Northern Society to death by quartering and thirty-one to beheading before sentencing others to cashiering or lifelong exile with hard labor. About 120 members of secret societies underwent extrajudicial repression including imprisonment in fortresses or transfer to active army service in the Caucasus.
The first party of Decembrist convicts began their exodus to Siberia bound for mines at Nerchinsk on an unspecified date following their sentencing. They traveled through isolated locales such as Berezov Narym Surgut Pelym Irkutsk Yakutsk and Vilyuysk where few Russians lived before settling near Chita in Zabaykalsky Krai.
On the 26th of August 1856 with Alexander II ascending to throne Decembrists received amnesty restoring rights and privileges previously stripped away. Their children obtained rights privileges even titles like princes though fathers' titles remained unrecovered in many cases while some chose returning west since financial inhibition prevented others from doing so.