I can't quite make sense of the description. Does one of the "satellites" have to be connected directly to the router?
If so, it makes no sense to me as the reception is good there.
As I understand it, it only makes sense to switch off the old WLAN and supply a Deco with Internet via cable as a starting point. This creates the desired fast mesh network. I don't think the Decos work well as old school WLAN repeaters.