Omega Rabbit [The Omega Rabbit]

The father was an utter monster towards his wife and daughter so he deserved his fate.
Lady Heather originally rejected the deal as the demon – when he appeared – killed her family during an orgy they were having, in the end though Lady Heather accepted the terms as the demon said he would bring back her family if she did.
The son is actually a nice guy (although he does have the occasional fight with his sister).
Its stated that if the females don’t perform the ceremony their souls would be taken by the demon as well as those of the men in the family. So, whilst the fate of the men is pretty much sealed, the women can still live on. They are required to perform the ceremony at least twice (once with their father and once with their sons – depending on how many sons they have). Once they have, they no longer need to keep performing the ceremony (so the mother can re-marry and have kids etc. without the deal looming over their head