@ahmedtuf 

Hi, for Option 1, the Deco could work both on wireless router and access point mode;

For Option 2, it needs to be on the access point;

As for the difference between router and access point, I suppose that you have seen the following link already:

https://www.tp-link.com/en/support/faq/2399/

Thank you very much.

@ahmedtuf 

Hi, did the current network map is like the following connection:

ISP router(Wi-Fi off)---main Deco---(WiFi)-----slave Deco 1

                                             \___   Netgear GS108---(cable)--slave Deco 2

The Ethernet backhaul of Deco is based on the standard IEEE 1905.1 protocol and have you checked whether the GS108 supported standard IEEE 1905.1 protocol or not?

If possible, could you please unplug the slave Deco 2, and check whether the other devices connected to the switch could get internet service?

Thank you very much and wait for your reply.

@ahmedtuf 

Hi, yes, currently, the second satellite living room Deco is on the Ethernet backhaul and the first satellite Deco is on the PLC and wireless backhaul;

And they are working properly on the option 1.

Thank you very much.