Sidney James is very nice! You have my total blessing on that one. hehe
I see
Sidney as an absolute unisex name, though... works fine for both girl and boy. Using a second name which clearly states the persons gender is advisable. -
James does that.
Madison is good for a brother. But again, needs to have a gender specific mn.
Mackenzie is nms, and
Morgan is too feminine imo. Also, with your combo of siblings, there are 3 M-names! Thats too much 'M' for my taste.
Except
Morgan, they are all totally unisex names imo, especially
Sidney.
Eartha is nmsaa!! sounds too much like earth (dirt).
How about:
Madison DominicSydney JamesQuentin LucasColin Patrick