WoW only consumes 56kb/s I've got 3mb/s Down and 1.5mb/s up. supports 2 people playing wow and then some. However, I still CAN lag on occasion and on different games. like in diablo 3 I get 120-400 latency as my average.
Your best bet get a simple 50mb/s connection. that seems relatively standard for multiple people.
Then comes into question that many people running. 2 running gaming. make sure you get a good modem/router. I am stuck with Verizon and I've got through 6 routers over a 2 year period so far. I now got one of their new models of d-link routers and it seems okay as they all do at the beginning. But, running that many people and gaming and downloading whatever it may be will stress a router a bit.
I haven't looked into this...