well, Killer Queen basically was the only stand that propably could have killed him.

Actually, the reason why they didn't use The Hand to kill his dad was because they didn't know what The Hand erasing power did to the things it erased. It could just erase him from existence, or it could just teleport him to somewhere else or, worse case scenario, teleport him into a eternal state of torture. So they decided to look for someone that had a more clearer killing stand power.