Is that the best you have? Really?
While we are under the impression, I don't recall it is ever explicitly stated (happy to be corrected)..in game, that Dom knows Cole is Kanes father. The only person 'at the time' who knew, was Alexander, Callista and Elana. We do not yet know exactly how old Dominique was when Veronica and Olivia were born. On the SecretSub path...Stefan tells Kane that all the sisters know that Cole is his father.
NOw, bear in mind, this is largely useless and irelvant information to Kane, he's never met him, doesn't know who he is....or anything else. So all you have is, Dominique is keeping the fact he is alive secret. Even if she told Kane...what? However, hehehe, Olicia, Veronica, Alessandra, Yvette (and Astrid though we'll not count her at the moment) all know Calista...is alive and well. His own godamn mother.
So in reality, even Dominique is more honest to Kane than his own damn mother is.....as for Jules being who she is, have I not already stated/said that cruelty has nothing to do with trustworthyness towards Kane? All the sisters bar Olivia (and nearly all the damn staff) are in the same boat here.