Remote management on OSX platform over the internet (dynamic ip)

Solution 1:

If you and your parents both have an Apple ID, you can use screen sharing via iMessage (Messages app).

Open a conversation w/ your parents, click on the "Details" link in the top-right corner of the Messages app window, then on the two screens icon, then on "Ask to Share Screen". Your parents have to confirm the request dialog with the option allowing to control their computer selected. This will open the Screen Sharing app and will allow you to control the remote Mac. You can even copy files to their machine via drag-and-drop from your local machine into the remote screen window.

Administrative tasks in the Finder can be performed in non-admin accounts by just entering admin credentials into the respective prompts (for instance, login/password dialog after clicking a lock icon in Preferences.app or when installing an app via Installer.app). Just add an admin account for you and a non-admin account for your parents.
Administrative tasks in the command line can be performed via sudo.

Additionally, for remote administration/access, you can try

• TeamViewer (free for private use) https://www.teamviewer.com/en/download/mac-os/

or

• Screens (ca. 35 € one-time license) https://edovia.com/en/screens-mac/

Both have methods/software components to work with dynamic IPs/behind a NAT.