Incest is too strong to called their sibling relationship. As for me who have watched the original, siblings relationship in FbC didn't feel like sibling. Their interaction isn't convincing enough as sibling.
Although i don't like romance between Ling Xiao and Jian Jian, but the reason why Ling Xiao develop romantical feeling to Jian Jian is understandable. He like being around her, he is a loner and can't get along with other peoples, hence his friend called him "god". Because no one can't reach him or communicate with him. Ming Yue can get along with him through Jian Jian.
Then Ling Xiao's feeling to take care of Jian Jian become out of his control. It developed more than just a brother. He is care to her, and she is his world, something that make him stay sane.
In FbC, there is no moment to highlight why or how San-Ha liked Ju-Won. His romantical feeling to Ju-Won didn't appeared suddenly, but the series also never give us any clue why, how, when? Maybe he never see her as sister to begin with, and just get used to her.
As from Ju-Won's side, the plot is even lazier. I know the series make them 10 years apart to reset their feeling to eachother, especially Ju-Won. So when they meet again, she can see him as a stranger. But still, us viewer only see it minutes apart, some minutes ago they're brother-sister then some minutes later they're lover.
In short, why some of us dislike it, because there is no moment to build their romantical feeling.
In Go Ahead there is scene when Jian Jian is mistaken Ling Xiao are about to leave China to Singapore. After that she realized her feeling that it hard for her to get separated again.
There is also a scene when Zi Qiu got in an motor accident, it make Jian Jian realized that she care for her brother.
There is no such scene or moment in Family by Choice.
