Zend certified PHP/Magento developer

One modem, 3 routers (3 access points) no connection between the routers

So, before explaining this is the situation drawn out:

  ------- Router_1 
  |
Modem --- Router_2
  |
  ------- Router_3

Three routers on 3 seperate floors of the building all connected to the modem (lan-cables through the walls attached to the modem). So that means 3 access points on each floor and there is no way to connect the routers to each other. Every time you go to a different floor of the building you manually change your access point on your device, i.e. phone, laptop, etc…

How do I, or can I even do it, create a “single access point” like in a Wifi-Mesh where it switches automatically to the stronges signal, without needing to manually switch between routers.