You may be getting interference from neighbouring wireless signals.
1)Change the broadcast channel on the router to channel to a less congested one than the current. You can download netstumbler or inssider (google them) and they will display the broadcast channels of any neighbouring wifi networks
2)Turn off any baby alarms cordless phones wireless doorbells as these use the same 2.4Ghz frequency
3)Update the firmware of the router and drivers for your PC/laptop
4) consider using power line, these use the household wiring instead of a long Ethernet cable. You plug 1 adapter into the Ethernet port of the router and local mains socket the other adapter into the distant PC/Laptop/game console and a mains socket. If you replace the distant powerline Ethernet adapter with a powerline wifi adapter you can create a local hotspot a good distance from the router.
5) if you are having 10 users in the same house you may be better getting your own router and plan. getting an extender won't help unless your signal strength is very low.