Complex setup (more channels, etc)

Hello, I have the following setup and need your technical advice.

1 central device that will receive all messages and geolocations from 15 separate devices and send separate messages to each of the 15 devices.

15 devices that will each be able to send and receive messages and their geographic location only on the central device. The 15 devices should not be able to see, send or receive information with each other.

The solution I have thought of so far is:

A custom primary channel on each of the 15 devices (different for each of the 15) in which they will be able to send and receive information with the central one.

15 separate channels on the central device that will each receive the geographical location and will be able to send and receive messages with each of the 15 separately.

Problems with the above setup:

The sub channels I can open are only 7. What should I change in the firmware code to be able to open 15?

Can the geographic location from the primary channel of the 15 devices go to the secondary channel of the central one? If not, what do I need to change in the firmware code to make this happen?

In the Lora config menu, how can I put Ignore incoming more than 3 values. For example, how can I put 15 values?

Take a look at LoRa WAN. This is not a mesh that you are describing and i dont think MeshTastic can help.