True those two are Oryxs daughters, and therefore Crotas sisters. One of them tricked Crota into opening a tear into another dimension while in their death realm, which the Vex came through, trying to build as the Vex do, they couldn't because of the altered logic of Oryxs dimension so the Vex created a new mind logic to understand the sword logic of Oryxs dimension, derived it must kill everything to be all powerful thus corrupting the Vex into what we now know. Also took the way the hive worship the worm and incorporated it into the Vex and made them worship a God. The black heart in the black garden. Oh and Oryx used to be one of three sisters. But after being killed and reborn and changed by the worm over 1000s of years..he is now a male king. And his sisters have separated themselves from him to make themselves more powerful because they couldn't grow with him being so powerful.