If you insert SIM card into your phone, does it work properly? Make sure it's working well firstly. What's the status of LED on MA180? Is there a utility on your desktop? If you have no idea about...

The middle light is the powerline light. If that light is off, there is no connection between the units. You have to repair them to get them connected. https://www.tp-link.com/us/faq-258.html

You can connect B and C router with Archer C9 to get internet. But you need to do the isolation settings on your Router A to make sure B and C can't communicate each other.

It seems it does NOT support this feature. We can only check that on the app.

How about the distance between the bulb and your wireless router? Try to take it close to your router to configure it.

What kind of application are you using on your computer? How you connect Roku to the router, wired or wirelessly?