When you create a new user on your site, you can untick the box that reads ‘Send User Notification’. That way the new user doesn’t receive an email about their account.
Also, when you create a new user, you have to set a password for them, and I believe the site admin would still receive an email notifying them of this password ‘change’, even if it’s a completely new password and it didn’t really change.
It’s possible to disable this password notification email with a filter. Here’s an explanation of how you could do that: https://wordpress.stackexchange.com/a/206396/92868.
One more thought: if you’re receiving duplicate emails, could it be that there’s a rule in your email client that duplicates certain emails? Or perhaps you have an email forwarder setup that creates a duplicate in some way? Just a thought.
I hope this helps. Good luck with it!