The participant name of the certificate contains the name of the itch.io username, so you don't need to register your name. The certificate will be given via Biga Discord, so make sure you enter the Discord to get the certificate after the jam is over
Viewing post in If you win, do all team members receive a certificate?
The name that will be written in the contents of the charter certificate is the username of the sender's itch.io account, so it will not affect whether you are working as a group or individually because what you will see is the sender's itch.io username. If each person (4 members of your team) sends the same game with a different itch.io account, you can be reminded that the name of the game sender with the itch.io username will be included in the charter. but is it permissible for 4 different itch.io accounts to take part in 1 game jam and submit the same 1 game?