Capture Packets between two bridged routers

Hi I'm having difficult time capturing packets from my home network. I'm connected to the router downstairs which is bridged by an ethernet cable. I'm trying to sniff another computer on the same router using my wireless nic card. I can see all of my traffic but not others. I can ping them and get a reply but nothing other than that. I'm also under comcast and lots of it is showing up in ipv6.

Home Setup

modem--ethernet-->Xfinity Router--ethernet-->Cisco Router-))wifi Com 1 Com 2 Com 3 All the Com 1 2 3 are on the Cisco router