Gerfenikss I am not sure why you seem to be personally attacked here or is it just your normal behaviour to attack anyone disagreeing with you?
I am not sure about the Details as I can't recall the game ever specifying this part of the story... it's pretty much "yeah so that's the situation your task is to stop them now"
??? this doesn't even make sense so I am not sure how to reply to you.
When the MC tries to free all the girls from the mind manipulation he always seem to fail as his skill is not strong enough for such a feat yet Lust managed that several times (with the Dark Elves and the Girls present in the Church).
There are several instances when the game tells the Player that the Twins rule over the other Demons as they are much stronger than the 7 deadly sins and for the sister that's one of the reasons she was so shocked that they not only lost in the church but that the brother was killed atop of that.
She seemed surprised about them attacking her at all since she thought to have concealed herself and her actions for them, the fact that she has to interrupt the ritual to fend for herself and even need to summon the Berserker Gluttony is more than proof for that, the ritual failing as a result is certainly nothing she prepared for aswell