"Antoinette possesses two doubles in Christophine and Tia, and Rochester finds his own doubles in Daniel Cosway and Sandi."
Robert Kendrick, "Edward Rochester and the Margins of Masculinity in Jane Eyre and Wide Sargasso Sea"
I've always liked the idea that we are all a combination of our influences. That idea is I think what Robert Kendrick is trying to get across in this section of his article.
Antoinette's doubles, according to Kendrick, are Christophine and Tia. These two characters are also the most influential for Antoinette. Her character is then likewise 'doubled' in them, or theirs in hers.
Rochester's doubles are Daniel and Sandi. Daniel is everything outside of what Rochester wants to be - almost an anti Rochester. But still Daniel is the one that believes in Rochester, or, as Kendrick put it, "Daniel Cosway believes in the fiction of 'Edward Rochester, Gentleman.'"
I agree with Kendrick. We are all a mish mash of our influences - we all have a certain number of 'doubles.'