Complex sentence: After they were vanquished, Gideon killed Sigmund when he was about to tell everything to the Charmed Ones, then sent Leo and Chris in a mirror dimension where Evil ruled, as well as Paige and Phoebe, to get them out of his way.
Split into simpler sentences: After they were vanquished, Gideon killed Sigmund when he was about to tell everything to the Charmed Ones. He then sent Leo and Chris, folowed by Paige and Phoebe, into a mirror dimension where Evil ruled, to get them out of his way.