RBR10 mesh. 2 routers used as one

Hello, I have a mesh system in my 1950’s house. Single story with full basement. Most of the walls are plaster with metal lathing which makes it difficult to set up a decent WiFi signal in the house. I think I’ve found the best locations for 2 satellites within the house for WiFi connectivity. My garage is unattached, sits around 60’ off the rear of the house. The garage has an Ethernet cat 6 line to it that operates well. I have been using a cheap router in there but I was hoping I could somehow double up the other RBR10 router in the garage as well. Same signal, same password type of thing. Right now, I’m having mixed results using the new set of satellites as the 3rd satellite is getting its signal from number 2 satellite in a window in the house. Sorry so long winded, is there a way to use the 2nd RBR10 router in the garage in conjunction with the house router via Ethernet cable? Obviously I’m not very learned with WiFi stuff so I apologize for my ignorance.

Patrick