@TIM_MESH_SYS Thank you for asking the community.
Woozle is correct. There would be no difference in connecting the third router to the network from that connecting the second.
Here is the guide for your reference to connect two or more routers into a mesh network:
How to add a router to an EasyMesh network as a satellite device
If you're building up a mesh network via Ethernet backhaul, you may refer to this guide:
How to Build an Ethernet Backhaul Using Two EasyMesh Routers
I hope you can make them work. Please let us know if you have further inquiries or questions.