I've only known one
Sidney personally, and that was a guy. Then there's
Sidney Poitier, who's also male. I think it works on both sexes and I see it as usable.
Sidney James sounds very nice, as it's good not to use a unisex mn, so there's no doubt about him being male or female.
Morgan,
Sidney,
Mackenzie, and possibly
Madison?
Morgan and
Sidney are good as brothers.
Madison is too feminine these days, imo.
Mackenzie is just nms. Together, with the four of them they might as well be sisters...
Eartha is nms