Yup. Other peoples internet activity will cause momentary internet connectivity saturation. And not just at the ISP level, but also in WiFi signaling as well.
If you must use WiFi and still provide a smooth connection, the easiest option is to just increase your ISP maximum download speeds. In addition, or in tandem with the first option, is to purchase a firewall that can prioritize traffic alongside quality WiFi hardware (such as an AP from Ubiquity).
....or, you can just shout at people to not use the internet when you are, but that won't make very good friends or a happy household