I need some help from the community. My home is a two-story family house built in a U-shape. I have an Archer C7 connected to the ISP modem located on the ground floor  - they are both at the end of the house in one leg of the U-shape. Connected to that I use two RE300 range extenders to extend the wifi to the other leg of the U at the opposite end of the house (not effective). I have an ethernet cable running to the top floor, connected to Archer A6  that provides both cable and wireless connections - there I also use RE300 range extenders to provide wifi coverage for the top floor. Supposedly the A6 and RE300s are part of a mesh network. I use the same SSID and password across the network to help with seamless connection anywhere in the house.

Problem is that wifi is inconsistent on the top floor and on the ground floor at the end of the house away from the main incoming access point. 

Any suggestions on a better configuration and combination of routers / extenders to provide better coverage over the entire house (bottom floor and top floor, both side of the U-shaped building)???