Regarding Wide Sargasso Sea:
I think Christophine was Mr Cosway- Antoinette’s fathers- Mistress.
It’s because of something Daniel/Esau said
Namely, that Old Cosway would give a bit of land and a hut to slaves he had sex with.
When Rochester writes to his friend, the friend states that Cosway gave Christophine a bit of land and a hut.