The suspects are Moroccan-descended Abderrahim Moutaharrik, 27, his wife Salma Bencharki, 26, Moroccan Abderrahmane Khachia, 22, and wife Wafa Koraichi, 23. All of whom were arrested in April.
The four-member cell was planning a terror attack on the Vatican during the current Jubilee year of mercy and also on the Israeli embassy in Rome and other locations in Italy, prosecutors say.
Moutaharrik, from Lecco in northern Italy, allegedly planned to carry out an attack in Rome on orders - sent via messaging service WhatsApp - from the IS.
He and his wife wanted to travel with their two small children to IS territory in Syria before Moutaharrik returned to Rome to launch an attack, prosecutors claim.
The Italian national is listed online as Switzerland's welterweight national champion for 2013 and 2014 and he has competed across Europe.
