Responses
Realistically, she was brought to the house at 9, and if it’s about marriage we can assume with the setting she is about 16-18, considering older time period marriage ages, so it was at least 7 years, so it wasn’t completely growing up together, but it was a big chunk.
Siblings but not related by blood... still kinda incest. You grew up side by side as ‘siblings’. A beginning full of misunderstanding that will eventually be cleared up later. Really just here for the smut as I can tell that the story is not going to be satisfactory.