Eris and the Queen were actually corresponding with each other pretty regularly. Eris is a part of Ikora Rey's Hidden, which is why at the beginning cut scene the Queen says "my Hidden friend." Mara Sov's origins are... tricky. There is no information regarding anything about her life before she captured the Wolves. It could be possible that she is related to the Hive, but she probably isn't Savathun, because Savathun is likely much more powerful than the Queen and would have put up a better fight.