@Bhaal 

Yes, you can have powerlines in their own group.

Here is how you would add a powerline to your existing network: https://www.tp-link.com/support/faq/1618/

@Tony 

Hello,
I try to explain myself better.

I find myself in this situation:

Powerline 1(EXT) ~~~~~~~~~~ Powerline 2(base) ----------------(LAN)---------------- Powerline 3(base) ~~~~~~~~~~ Powerline 4(EXT)

Legend:

~  Power lines

- LAN

Power lines 1 and 2 are bind and power lines 3 and 4 would be bind.
Power lines 2 and 3 would be connected via an Ethernet cable

Powerline networks work fine when the LAN cable is disconnected, but when I connect the cable one of the two powerlines becomes unreachable and not pingable.

I've tried using two different network names, but it doesn't work

Thx

@Bhaal 

That will not work, you will create a network loop. It would be the exact same thing as connecting LAN port 2 into LAN port 3 into your router with the same cable.