One of the more misunderstood data points is home internet "speed". The more accurate term is capacity. A 5 Mbps Youtube stream is not faster on a 100Mbps connection than a 50Mbps connection you can just handle more of them simultaneously. Here are some general measurements

HD Youtube or Netflix Stream = 5Mbps
4k Stream = 13-15Mbps
Home video teleconferencing = 4-6Mbps

This means with a 50 Mbps connection you should be able to manage multiple streams and still talk and do video. A key congestion cause can be game and software downloads and file sharing (bittorrent). Tell the kids to download the latest from Steam overnight not during the day.

One of the best things you can do to increase performance is get a new router. Some of the old, cheap, routers maxed out at 25 Mbps.