Thanks for the reply, I assumed that it was his bandwidth. Is there any way to remedy this? As in change ISP, or get a better router/modem or is the only solution just having one person on at a time?
The answer to that is not necessarily simple.
The first thing is what level of overall use is needed.
If everyone is only surfing webpages and doing other low use data tasks, then it might be fine as it is. After all, unless you are browsing to some REALLY graphic loaded web page (i.e. loads of larger size images to download), you should nominally no notice much difference between 5 Mbps and 100 Mbps when just browsing a web page. Of course, even with low data usage type stuff, you will reach a point enough people using those low data usage things will still add up to a decent amount and still potentially overload a 20 Mbps connection...and you likely will start to encounter some of the other factors that I alluded to (i.e. how well your router can handle all that traffic, etc).
If OTOH, there are several devices at a time that are streaming video, then 20 Mbps can get tight real quick. The quick and easy fix for that is more bandwidth (i.e. increase the 20 Mbps) if possible. If your friend is using satellite, then that may not be possible. And there might not be other ISP options if using satellite...most people who go with satellite tend to because that is their only option.
Just as a side note, the other reason more bandwidth can be useful is for downloading rather large files. This is likely where people get the urge to think in terms of speed. The more bandwidth/throughput you have, the faster you can download that large file. I have a connection that is officially listed at about 70 or so Mbps if memory serves, but I can frequently get up to about 90 Mbps. I can download a 5 GB file in about 10 to 20 minutes if memory serves.
Now, there can be other factors as I alluded to.
For example, if there are enough connections, especially over WiFi, then you might encounter bottlenecks from that. Your typical router cannot actually handle simultaneous traffic...it can only handle it one at a time. It can do so quickly that is seems like it is doing it simultaneously, but it is just serving up small chunks to each device in turns (your Internet connection is not a single piece of data but rather little chunks). If there are relative few devices, then there will be no lags and it will like it is simultaneous. As you get more devices, the cycle of one turn gets longer, so each device has to wait a little bit longer with each added devices for its turn of chunks of data to be sent or received. MU-MIMO is supposed to help with this on WiFi, but MU-MIMO is relative new and not all WiFi routers support it...and any device that connects to that router and wants to benefit from MU-MIMO would also need to support it. The other factor is the processor of the router. The faster the processor, the faster the router is able to serve up the chunks of data to each device.
So, the short answer is you first likely need to truly figure out where the bottlenecks might be and address them. There is a rather good chance that at least part of the answer is to get a "faster" Internet connection (aka get more bandwidth/throughput). That may address the issue, but you may then find there are other factors to address.