assuming all 3 tv's are streaming at once and a 4th person is gaming at the same time would be a guess of about 50 mb/s. i'm going with suggested 10 mb/s per tv stream and 20 mb/s for game system. all are high estimates really but 50 mb/s is not exactly top of the speed range anyway. pretty much entry level.
so if you are looking at 70 mb/s anyway, then you should be good to go. of course if you need more speed, you can always upgrade your package down the road.