Setting up Family Sharing/Apple ID without using school email
Why would you do this? When creating an Apple ID you are also creating an iCloud account. Just use the iCloud email generated as part of the process, or create a new email address for this purpose using any other free email service of your choice such as Gmail. (If you state he is underage, Apple will force you to use the iCloud email and will not allow you to use a non-Apple email for the account.)