I think take last anon was actually asking why HIC wanted to kill the Alpha kids. Just so that anon knows: HIC thinks humans are disgusting. She eliminated their entire race during Dirk and Roxy's time, beside those two. She wanted to kill them to finish the job and also to get them out of her way during their game session.

The Condesce needs the kids to finish their session because her goal is to escape to the new universe and hatch the matriorb and rule over the new population of trolls. She sent droids after Dirk and Roxy when they were on Earth to force them to enter the Medium and play the game.