hi @Harish-kumar , we released here Lora-Mesh, that I thought it will help you.
Well, mesh-network over LoRa, has a specific protocol (Thread), and probably it's not implemented neither in Arduino, nor Multitech.
This would work if all 3 devices would be Lopys, the last one (gateway) would be registering itself to TTN as gateway, and forwarding data from the first Lora (sensor), thru the second one (the repeater, which does this automatically, being a Mesh node - router role).