I wish to establish a well functioning wifi in family's summer house, consisting of two buildings next to each other.

Currently, I use 3 mesh points: A) where the modem is located, on the eastern side of the eastern building, B) on the far western side of the eastern building, and C) on the far eastern side of the western building. The distance between B and C is approx. 10m.

The signal on C is quite variable. Sometimes the wifi drops out, and sometimes it works fine. I need a solution to get a more stable wifi in the western building.

Would Deco X50 outdoor mounted on the outside of the western building be a solution? Does this become a part of the mesh, or is it more like an "end-point" that cannot be further extended? 

https://www.tp-link.com/no/home-networking/deco/deco-x50-outdoor/
 

Other solutions?