Use USB Tethering for local router as internet Gateway

I want to use a local router as a node for all devices to connect to internet instead of Android Hot-Spot.

Reason: Because connecting to Android requires manipulating the NAT on multiple phones just to connect two devices with each other and there are multiple devices.

Attempted Solution:

1. Connected a phone to WiFi that has internet (to act as internet gateway for the router instead of of the regular cable)
2. Connected the same phone to the router using USB-Tethering from phone, the USB Port is working fine (the LED is giving green color indicate that) but the internet LED gives red color (Indication that it is trying to detect internet gateway) but it never turns green.

What am I missing or should look up at the internet because I failed drastically?

Similar Problems to mine:

1. Using cell phone as Internet provider for router
2. Cell phone as data feed to wireless router
3. Use Smartphone as gateway to internet for my local network (Not smartphone hotspot!)

Some Information that might be helpful or relevant:

1. I have multiple PCs that can only be connected via LAN (They are far from each other to the extent that not even a Wi-Fi Module can connect them to the router)
2. Router Type: ZXHN H168 V3.1
3. Thought of making a device act as the gateway but then, I am not sure if the devices are going to communicate with each other nicely (without needing to manually edit the NAT) & do not know how to do so and not to mention that the only device capable of doing this is a laptop because it has both Wi-Fi and LAN.
4. Image of the entire connection described above