tl;dr – No data is sent anywhere, except between you and Google.
No matter if you use my templates or create your own copy of my script, I will never gain access to any of your data.
You are in full control of all the data. The scripts and addons are only accessing data you yourself have access to. No data is sent anywhere, except between you and Google. All data reading and writing is done by you on your own account.
For add-ons like SPOGOU this means all data is read and written in the Google Sheet you created and own. The add-on reads and writes to the Google APIs on your command, and only reads the group members and updates the passwords of the users that you have delegated admin access to and authority to update.