So my extender is creating a separate network. There are three wireless networks listed now.
2 2.4G connections and 5G
We believe that the extender is creating it's own network. Is it normal that we have to switch back and forth between the 2.4G networks if we're in separte parts of the house? Or should we have one network to sign into without having to switch?
I don't think the extenders support handoff technologies like 802.11k/r/v fully, so by default they end up creating separate SSIDs on the assumption that most devices won't be moving. If you log into the extender's web interface (you can retrieve the IP address of the extender from your router at http://192.168.1.1/ ), you should be able to rename the SSIDs broadcasted by the extender to match.
Some devices will automatically roam in a best effort manner when two different access points broadcasting the same SSID are detected. Other devices may end up being sticky, and will require turning Wi-Fi off and back on in order to join a closer Wi-FI access point. For stationary devices, the only problem I see happening is that a device may latch onto a further access point and not roam, which if the signal is marginal to that further away point, will result in a poor experience. Either way, worth changing the names to match and see how it works out.
As for the network extender, it's creating a separate "SSID" as it's called, but it's likely not creating a separate network. If your devices can maintain the same IP address whether they are on the router or your extender, that would be the same network. If IPs change (such as 192.168.1.10 to 192.168.2.15) then you have a different network.