unable to wirelessly connect to a new home network

My problems began because our ISP (Cox Comm.) informed us that our modem was out-of-date and needed to be replaced, so I bought a new modem (Motorola/ARRIS SB6121 DOCSIS 3.0 CABLE MODEM) and a new router (ASUS RT-N66U Gigabit Router Wireless-N900) to boot.

I've been able to connect our iMac & MacBook Air but not our 2 iPads (MC775LL/A & MD417LL/A) and 2 iPhones (Both are (Model # MC924LL/A).

Since they're all older models, we're continuing to use iOS 7.1.1 rather than to upgrade to 7.1.2.

Would it help to connect each wireless device (1 at a time, of course) to the primary computer and then try again?

Once I get those guys up and running, then I can tackle connecting to our TV and DirecTV service. Whew!

I'm not sure which community is the best choice for this issue but the Apple support communities have come to my rescue before, so I'm optimistic someone will help me get through this.

Thanks-

Linda M