Encryption can’t protect you from adding the wrong person to a group chat. But there is also a setting to make sure you don’t.
You can add your own nickname to a Signal contact by clicking on the person’s profile picture in a chat with them then clicking “Nickname.” Signal says “Nicknames & notes are stored with Signal and end-to-end encrypted. They are only visible to you.” So, you can add a nickname to a Jason saying “co-founder,” or maybe “national security adviser,” and no one else is going to see it. Just you. When you’re trying to make a group chat, perhaps.
Signal could improve its user interface around groups and people with duplicate display names.
I would say don’t teach them how to use Signal, but they clearly don’t read anyway so fuck it.