@Pip60 

Hi, the Deco P9 could use the powerline and wireless backhaul together.

And you don't need to remove the original powerline adapters from the network and if possible, you could consider plugging the powerline extender into the Garden office to extend the Deco network.

There is one more notice even though the Deco P9 could work together with powerline adapters, there would be no powerline backhaul between them;

Thank you very much.

@Pip60 

Hi, it is ok for you to have more than 3 Deco P9 in the same Mesh network;

The previous suggestions about the powerlilne adapters would also give you wireless access as long as the powerline adapters have the wireless ability;

(ISP modem--Deco P9~~~~plc backhaul~~~~~Deco P9-------cable------master powerline adapter~~~~electric wire~~~wireless powerline extenders;)

Thank you very much.