Well as suggested above you could get a trial of NOD36 and also when you are at the AVG stie get the free spyware program. Also you may want to consider getting these free tools. (just google them)
hijack this
Search and destroy
ZoneAlarm
Hopefuly if you get these it should stop this from happening again. Also there is programs out there which could stop your cousins from going on those types of sites.