RT-N66u high ping issue

Hi guys,

I've been having this problem for the past two months or so. Whenever anybody in my household connects their iPhone to my WiFi network, I get insanely high ping spikes for a minute or two. I have noticed that Android doesn't cause this problem, as I own a Nexus4 and never experience this whenever I connect to WiFi (same with my father, who owns a Galaxy Note 2).

For example, this just happened a few minutes ago. I'm at home using a wired connection, my brother comes home, his iPhone connects to our WiFi network, and all of a sudden ping spikes:

Tracing route to www.google.ca [173.194.43.120]
over a maximum of 30 hops:

1 <1 ms <1 ms <1 ms 192.168.1.1
2 1424 ms 1440 ms 1467 ms 10.125.23.1
3 1538 ms 1544 ms 1327 ms 24.156.137.233
4 1448 ms 1457 ms 1099 ms 24.156.146.1
5 696 ms 803 ms 943 ms 69.196.136.68
6 911 ms 1014 ms 1168 ms 72.14.212.134
7 1113 ms 1124 ms 1045 ms 209.85.255.232
8 1216 ms 1107 ms 1089 ms 72.14.239.73
9 1336 ms 2964 ms 1522 ms 173.194.43.120

Trace complete.

Pings will then go back down, usually after a few minutes:

Tracing route to www.google.ca [173.194.43.120]
over a maximum of 30 hops:

1 <1 ms <1 ms <1 ms 192.168.1.1
2 6 ms 7 ms 7 ms 10.125.23.1
3 13 ms 7 ms 16 ms 24.156.137.233
4 9 ms 12 ms 10 ms 24.156.146.1
5 10 ms 8 ms 9 ms 69.196.136.68
6 13 ms 9 ms 15 ms 72.14.212.134
7 19 ms 22 ms 12 ms 209.85.255.232
8 9 ms 14 ms 9 ms 72.14.239.73
9 21 ms 10 ms 8 ms 173.194.43.120

Trace complete.

If I block their devices from connecting to WiFi (using the MAC filtering), this issue never occurs. I tested it by blocking their devices mid-spike, and pings will immediately drop to normal levels.

Any ideas what's causing this? Is it some of their apps downloading a bunch of crap when entering WiFi range or something? Could it be the way I have WiFi set up on the N66u?

Also, my speeds from my ISP are 30down, 0.5ish up.

Thanks for your assistance.