Actually, its action by the National Assembly which lifted Guaido's immunity from prosecution.
This is the same group of legislators that elected Guaido to lead them several months ago.
No. The National Assembly supports Guaido. The Constituent Assembly (Asamblea Nacional Constituyente: ANC) is the Maduro construct. From Wikipedia: ‘On 8 August 2017, the Constituent Assembly declared itself to be the government branch with supreme power in Venezuela, banning the opposition-led National Assembly from performing actions that would interfere with the assembly while continuing to pass measures in “support and solidarity” with President Maduro.’