Complex sentence: Madelin, 422 Barère, Vadier, and Stanislas Fréron joined the accusations against Saint-Just and Robespierre; the arrest of Robespierre, his brother Augustin, and Saint-Just was decreed, along with that of their supporters, Philippe Le Bas and Georges Couthon.
Split into simpler sentences: Madelin, 422 Barère, Vadier, and Stanislas Fréron joined the accusations against Saint-Just and Robespierre. The arrest of Robespierre, his brother Augustin, and Saint-Just was ordered, along with that of their supporters, Philippe Le Bas and Georges Couthon.