I honestly can't see why people mind either of them. The fact that Charlotte is rather nice to look at helps in her case though.
I definitely got the impression that that might be the case; Ben likes to give off the impression that he's in control of everything, and since he's good at improvising, he usually manages to pull it off. That said, it's impossible to tell these days; it could credibly be any of a number of people. Personally I think the most likely suspects are Sun, who would just want to rattle Kate, and Claire's mother, who would have the most obvious reason to do it (her denial could have been a lie).
Charlotte was apparently born on the island as well; she made some comment about "returning home" either earlier in this season or towards the end of last season.