Serviio

If you are using each router as a stand alone network, it's going to be difficult to impossible to get the routing to work between the three different networks. That's because each network is going to be on a different IP address range, and by default multicast and uPNP packets will not cross different address ranges. You can't just disable the DHCP services on floor 2 and 3 unless the routers are in Access Point mode.

My suggestion is to redo your network, making the entire network on the same IP address range. Where does the Internet enter your home? Let's use the first floor as an example. The router on the first floor has the WAN connection to the Internet, and performs your network DHCP and DNS functions. There is an Ethernet cable that runs to the 2nd and another to the 3rd floor. The routers on floors 2 and 3 are placed in Wireless Access Point mode. You will need to enter a static IP address in each of those routers (to make it easier for accessing the settings), and the Ethernet cable from the first floor is connected to their WAN port. For wireless, you can either use the same SSID and password in all three routers, or you can use different names for each floor, to better identify which one you are connecting to.

You now have one single network for the entire house, and Serviio will work on all floors.