@GCConsulting 

With Deco X90, the only way to do what you want is by connecting Office Deco to Living Room Deco with Ethernet cable.

Using powerline adapters as a substitute to Ethernet cable connection might work, too, but they do not deliver fast speeds. 

If you happened to have TV cable between Office and Living room, you could use MoCA adapters to have Ethernet over them and can connect your two Deco through them.