If you follow the guide Sasschary included and go turn on QoS and set all devices to normal priority the router should ensure that everyone gets a more or less equal part of the internet. But high load always equals to problems with the net and when everyone is on it trying to do stuff it's more or less unavoidable that you'll experience a slower net. QoS should help against if someone is trying to hog all the bandwidth though.
The drawback of setting a max bandwidth usage would be that neither of you can utilize the full speed of the net even for short bursts such as loading a web-page so I'd start with just using QoS if I were you and then talk to everyone about respecting the needs of others while on a shared network, maybe setup some rules about what's allowed. Also, when someone is alone on the net, they would not be able to use the full speed to quickly download something before everyone else gets home.
Also, go change the password for the router since Netgears default is admin - password. So it's not easy for anyone to log in and set QoS on their computer to higher. - If you find that it's already enabled, just figure out what computer is set to high priority and where that computer is connected and you've found that someone who has set rules to give themselves more then the rest.
However, your problem is most likely a result of there being less bandwidth then is required for everyone to do all that they want.
Ex. Streaming in 60FPS 1080P can use upwards of 10 mbit/sec depending on bit rate. If everyone is trying to watch at the same time at that quality you'd need 40 mbit/sec + download speed.
Here's some more info about setting up QoS
P.S. I do not claim to be an expert at this, just trying to help you as best as I can.
Edited by Vicin, 08 April 2018 - 07:37 PM.