These days 1Mbps is SLOW for one computer, let alone four.
QOS can help, but its only for what's going OUT from your router, not whats coming in. Think of a highway with a traffic light. The light can control what cars get onto the highway, but can't control what cars come off the highway, that's how bandwidth limiting or 'traffic shaping' is done. Traffic shaping is what network people call what you want to do.
I've done quite a bit of research on how to setup my linux router to do traffic shaping to be able to use my bandwidth most effectively, and what I've learned is that by sending certain requests out before others can have an impact on how 'reactive' your browsing can be, but with no appreciable speedup to your overall network speed. Quite the opposite, your really slowing down things to be able to speed up everything.
If your router supports it (what brand / model) QOS can help, but it won't fix the speed issue. I'd make inquires into a faster connection, or do some social traffic shaping so that one person is using the link at a time.
AS someone19 mentioned having 4 systems sharing a 1Mbps connection is the root of the problem and adding traffic shaping is probably going to only slow all of the speeds down instead of make yours more useable at their cost. -- even a single system on 1 Mbps is going to struggle nowadays on youtube etc. since they've increased the video resolutions so that more bandwidth is used since the standards have increased and more people are using higher rate connections.
Between the four of you can you come up with a few extra $'s to increase the connection speed from your ISP ( we use U-verse and going from 3mb\s to 6Mb\s costs only $5 more a month and going from 6 to 12 (which is what we currently use) is another $5 so for $10 a month we get 12Mbps instead of 3Mbps (they no longer even offer a 1Mbps service !) -- We used to have 18Mb\s but found we never really used more than the 12Mb\s offered and it was $10 less to drop to 12Mb\s. ) and figure $10 a month split 4 ways is only $2.50 a piece which should be doable (Or even you putting in the $10 to improve everyone's speed including your own would probably be a much better option than trying to cut their speed down so yours can improve !!)
You could try to QoS the traffic. Even though you can't control data coming in, if HTTP/game traffic gets higher priority, the ACK packets for other protocols will not get send out in time and that will cause the download speed to reduce for the other programs.
If you friends are doing P2P and you have a cheap router, the state table may be getting too large and that can also cause massive slowdowns.
Most low end router can only support 200-500 connections before your internet slows down. You could have a 100mb internet connection, but if you got even slightly over your connection limit, your router could be limiting you to sub 1mb speeds.