Linksys Router Help

I have a Linksys WRT54G Version 8 And upgraded my firmware to Firmware: DD-WRT v24 (05/24/08) micro in the hopes that I could set bandwidth restrictions for my mother and sister. See, we have 75 kb/s DSL from verizon. My mother and sister REALLY LOVE to youtube stuff as im in my gaming sessions. My question is, HOW DO I set their computers to only use maybe ..~ 20 kb/s of my internet so I can freely play my online games? QoS did nothing when i entered their MAC ID's and IP's. Im connected through LAN, they are wireless. Infact, they download stuff FASTER than my computer connected through wired does. I also have the TCP_VEGAS script:

echo 0 > /proc/sys/net/ipv4/tcp_westwood
echo 3 > /proc/sys/net/ipv4/tcp_vegas_beta
echo 1 > /proc/sys/net/ipv4/tcp_vegas_cong_avoi

But they still make me have lag spikes and make my gaming sessions obsolete. If anyone can tell me how to do this, that would be great. Google makes my life a misery when trying to learn QoS. Can someone give a noob some help??