Khentkawes I's family relationships are unfortunately purely conjectural. All we can say is she was important and powerful and identified with the Fourth dynasty. Who her father, husband and son or sons were we don't know. It seems safe to assume she was the bridge between the Fourth and Fifth Dynasties given the location of her tomb and use of her name by later queens but exactly how we don't know.
As for the succession father to eldest surviving son seems to have been the rule but biological failures and other circumstances sometimes made things more complicated.