Ok if you really need the Orbi to be primary you will need to get the set-top boxes IPs from the Orbi.
Log into the G1100 and go to My Network > Network (Home/Office) > Settings. Once into the properties go down to IP Address and change 192.168.1.1 to whatever the IP range of the Orbi is giving out. Next go down to IP Address Distribution and change DHCP Server to Disabled.
Once that is complete you will need to reboot you set-top boxes and they should start getting IPs from the Orbi and your G1100 will be acting as a MoCA adapter. You should be able to use the FiOS TV App once everything is reconfigured. But just so you know the is zero support from Verizon in thing setup. They will only support the G1100 as primary.