After adding new extender two TP-link wifi networks appear, but one has no internet connection
I originally had an AV500 4220 extender ethernet-wired to my router, and a 4020P extender ethernet-wired to my son's gaming PC in a different room. I'm not certain that this set-up was correct but it worked ok for the PC.
I wanted to improve wifi so I got an AV600 kit with a 4010 adapter and a 4220 extender. I now have the 4010 ethernet-wired to the router, and have relocated the old 4220 to a socket in a different room. I have paired the old 4220 with the 4010. The new 4220 is also in a socket and I tried to pair that also, but now when I search for wifi networks I get two options starting with 'TP-link '. One of these is the old network which will connect to the internet. The other is the new network and will not connect to the internet, but I can't get rid of it.
What I want is to have the 4010 and the two 4220's and the 4020P all on the same network. How do I get to that? Thanks.