our x55's are not working very well in the garden room. plan attached , room is number 1 main deco x55 is attached to the router at A two other deco are at x and 2 M4R's are at "o" Deco units are not

Hi All advice gratefully received. I have purchased a Deco x55 mesh system to replace my existing Deco M4R units. We have just had sky internet upgraded to 1gb speed and want to get a stable connectio