@David-TP 

To answer your questions:
 

cable modem? UBEE UBC1322 (as provided  by Optimum Online)

Is your network diagram like:

Cable Modem (4 ports and two phone jacks telephone) --> Main Deco  (coming off Port 1 on the cable modem) directly to the Main Deco)

                                                                                             --> 2nd Deco (coming off Port 2 on the cable modem) directly to the 2nd Deco
                                                                                            --> Unmanaged 1GB 8port Switch coming off Port 3 on the cable modem

                                                                                                                    Unmanaged 1GB 8port Switch   --> 1 PC (not connected to wifi, only LAN)

                                                                                                                    Unmanaged 1GB 8port Switch   --> 2 Lapops (not connected to wifi, only LAN)

                                                                                                                    Unmanaged 1GB 8port Switch   --> VOIP device for telephone service

     
Do you set Deco X90 into Access Point mode? No, both are in router mode

Thanks

Bernard

  @David-TP 

This makes no sense to me. If I use access point then I lose parental controls and basically all the features of the router and it is no longer a mesh system. What is the ideal way to get the backhaul over the wire and maintain the two broadcasting routers? Do both routers need to be plugged into the switch and the switch simply into the cable modem? 

The entire idea of this router being sold in a pair is to create a true mesh network, and to have a backhaul that is not going to share a wireless connection. If the switch is behind the cable modem and one device is connected to the switch while the other device (main) is connect to the modem directly wouldn't that allow the backhaul to work wired instead of wireless? Can you connect the 2nd port on the main to the 2nd port  (1GB) to each other and create a wired backhaul? There has to be a way as it has the option. If you can provide some sort of graphic that shows how I can achieve this it would be great.

Thanks

Bernard

  @Bernardhny 
In Router mode, one Ethernet port of the main Deco must be exclusively used to access Internet, no other traffic can come on that port.

Suggestion (not sure about your VOIP device):

Cable Modem (4 ports and two phone jacks telephone) -->  VOIP device for telephone service

                                                                                              --> Main Deco  (coming off Port 1 on the cable modem) directly to the Main Deco)

                                                                                                               --> Unmanaged 1GB 8port Switch coming off Ethernet on Main Deco

                                                                                                                    Unmanaged 1GB 8port Switch   --> 1 PC (not connected to wifi, only LAN)

                                                                                                                    Unmanaged 1GB 8port Switch   --> 2 Laptops (not connected to wifi, only LAN)

                                                                                                                    Unmanaged 1GB 8port Switch   -->  2nd Deco 

Even in access point mode, you would have the benefit of a mesh: one single wifi network, transparent roaming.

Having two cascaded routers (the modem and the Deco) is not always beneficial.