Router and Extender Setup

Ok, I'm tired of hitting my head against the wall. 

I have Verizon Fios that I am using for internet only. About 3-4 months ago I set up my Nighthawk router (AC3200 R8000) as my exclusive router and removed the Verizon router. I also connected my wifi extender (AC1900 EX7000). At least that is what I believe I did. I have my router connected via ethernet from the ONT from Verizon to the router. I have the extender connected via ethernet from a port from the router. Here's the problems:

1. My internet seems unstable at times. All my TV's are connected via ethernet. I checked via Nighthawk app for updates to the router and is up to date.

2. My wifi signal drops and reconnects every 30 seconds or so. I could be in the room where my extender is and I still won't get a stable wifi connection. This seems to be the case when I use devices that have their own network such as my mobile phones or tablets. Other devices such as Alexa, video doorbell, and thermostat doesn't seem to lose connection.

3. When I go to the Nighthawk app, I don't see that I am connected to my router.

4. When I setup the extender I don't see the NETGEAR_EXT. However, the signal lights on the extender are showing green.

5. When setting up the extender, I connected the extender near the router. I plugged it back in the spot I wanted the extender. I logged into the extender IPS and manually logged it in to the router since I wasn't seeing the NETGEAR_EXT. Not sure if I did things right. 

I don't want to use Verizon's router. But having the wifi drop constantly is driving my family and me crazy.