New gateway set up and identifying many devices I don’t recognize

It's unlikely that there are devices listed that are dangerous, well, unless you've given the wifi credentials to some Bad Guys who are camping outside your house.  It's not easy to determine the device but generally I use the MAC address given and check it against a database like THIS one. 

But that only gets you a manufacturer's name and often times it's still not enough to ID the device.  For instance, I have a DirecTV Stream Osprey box.  But its MAC address shows it as Wistron Neweb Corp, probably because Wistron makes the networking chip for it.  I have an Ambient Weather weather station but the MAC address comes back to Espressif.  This issue affects a lot of IoT devices.

Then there's the issue of devices like many phones and tablets that use "randomized" MAC addresses for security.  The address for your phone might change every time you leave the wifi area and return.  None of the randomized address will return any manufacturer.  That may be what is happening with your Apple devices, they're connected but the gateway can't ID them properly.

And finally, these lovely AT&T gateways have shown a propensity to just make up devices. 

Thank you, Tonydi…..that’s about what I expected to hear.  It definitely makes sense to me and I appreciate the info!