@AceRumble 

I assume you've set it up correctly, like this, https://www.tp-link.com/us/support/faq/1504/https://www.tp-link.com/us/support/faq/1504/

If so, then what is the IP Address of the Router?

Your devices, what is the IP Address they each get when they do connect? Are they the same or different?

I've never used a mobile router, but once you connect, it should supply via wireless a LAN with 2 SSID's, the 13FC's, one being a 2.4 Ghz signal and the other the 5 Ghz signal.  Those are the 2 you see.

I don't know why you can't connect one or more devices to either of those SSID's? The only reason I can think of off hand is IP Address collision? That is both devices are asking for (from the device settings) the SAME IP Address (192.168.0.100 for instance)? If this is done, the last one asking for the address gets it and the other device is dropped off.

What did you have before to use?

Might want to look at this FAQ links as well:

https://www.tp-link.com/us/support/faq/2028/

https://www.tp-link.com/us/support/faq/2041/

https://www.tp-link.com/us/support/faq/2031/

Sorry, not familiar with most of the technicality of your reply, went with this router specifically because it appeared to be simple. In practice, however, If I put setting to Client, all devices detect the wifi network but I can only connect one at a time to the ethernet. If I put setting to Hotspot, all devices claim that there is no ethernet connection on the network and am unable to connect anything at all. Setup is straightforward so I can't see where that is going wrong. My wired connection is through a Motorola surfboard cable modem if that makes a difference somehow. My internet provider was only able to provide the same reference to FAQs and setup as in your reply, both of which I have gone over and can't find anything that matches this issue. But provided the problem is an 'IP collision" as you suggested, what would be the fix? Thanks for your patience!

@AceRumble 

Yes, there is a SINGLE Ethernet connection on that device (router WR902AC ).

See these two links for the setup guide and manual:

https://static.tp-link.com/2019/201902/20190203/7106508201_TL-WR902AC(EU%20US)_QIG_V1.pdf

https://www.tp-link.com/us/user-guides/tl-wr902ac_v3/chapter-2-connect-the-hardware#ug-sub-title-2

To me, the "Quick Install Guide" can send you in the wrong direction. The 'At Home' section is not really correct. There is NO 'Router Mode' listed, it is in the 'During Travel' section. However, in the User Guide, section 2.1, it is listed there:

=============

2.1. Standard Wireless Router Mode

Create an instant private wireless network and share internet to multiple Wi-Fi devices. This mode is suitable for hotel rooms and home networks.

=============

That is the one you want.

You'll find the SSID's for Wireless on the bottom of the router. Yes, only a single Ethernet connection available. You can use a 'switch' to get more though probably. Here is a picture, https://www.dummies.com/computers/pcs/how-to-add-ethernet-ports-to-the-network/, but what you do is connect the wired devices to the output of the switch and the input of the switch connects to the router. These are fairly cheap and come in many port counts so many devices can be connected at once.