I dislike the name
Charles, because I find it uncomfortable to say, if that makes any sense. Just too many consonants ... It really needs a very
Royal Family-style accent to sound quite right ;-) For that reason, I prefer it as a middle name. Having said that, I do love
Carl. Of the combinations you gave,
Charles Emmett sounds best I think - but I'm unsure about using surnames as middle names, simply because people will assume they are family names. But then again
Emmett might be one for all I know.
Sidney is nice, but a little aristocratic sounding, so I feel it needs a down-to-earth middle name to balance it:
Benedict,
Edmund,
Theodore and
Bertram are probably too much, at least for my taste.
Sidney Ciaran has excellent flow, and imo it's the best, followed by
Sidney Jonathan,
Sidney Joseph and
Sidney David in that order.
Darcy is one of my favourites too. How about ...
Darcy CarwynDarcy TobiahDarcy BennettDarcy MylesDarcy Nicholas - This is probably my favourite. Although
Nicholas isn't my favourite of these names individually,
Darcy is quite gentle sounding as far as boys' names go, as well as unusual, so I feel it needs something (a) masculine and (b) well-known to complement it.