So I have the next configuration:

My main router is my X50 in my garden. The 3 other ones are on all my floors of my house pretty much above each other.

Distance from the garden to my house is about 14metres. 
Connection is very weak (yellow in the app)

What can I do to improve all connections as we lose the internet connection many times. 
Download-speed in the garden is 450mbps but in my house only 20mbps while I'm next to one of the m4r's, so thats a very big difference....