Airport Extreme (Bridge Mode) won't connect with all devices
I just purchased a new Airport Extreme (2015) to offer a better quality wifi signal in our living room and to connect our Apple TV and PS3 with a network cable to the internet.
Internet comes through a modem/router and splits off to the Airport Extreme in the living room and a Time Capsule on the top floor.
I installed it as a new network, not extending, and copied the settings from the existing network in our home. In Airport Utility all lights are green. I can access the Time Capsule on the top floor from the living room. Apple TV is working fine and so are many of our devices.
However, my wife's iPhone 6 and a 2012 iPad 2 cannot connect even after updating the iOS to its latest version 8.4.1.
When I switch the router modes of the Airport Extreme and Time Capsule to "DHCP and NAT" mode, all the devices can connect but I cannot reach my the Time Capsule on the top floor when accessing the wifi through the Airport Extreme in the living room downstairs.
What is going wrong? Do I need to work with Static IP's for the devices or the Airport Extreme and Time Capsule?