If you are using a HUB, it could well be your younger brother. And all he would need to be doing is streaming a Youtube video. HUB has no QOS so packets get sent as they arrive at the HUB, so gaming packets take their turn with all the other data, instead of being prioritised like a higher end router would.
Lets test it- switch of the WiFi, unplug everything except your PC, play a few matches. Problem gone? Its lack of QOS. if NOT, its another issue, post back and we can troubleshoot further for you.