Who's whom hmm?

They are definitely siblings, there's no doubt, but can you tell (without peeking) which one is which?
The first thing Hazel said when she saw Max was "he looks like Sydney." Looking at the pictures I think even Max would agree. Although this will probably be the first and last time he will allow any comparison between him and a stinky old girl. Related or otherwise.
By the way, if you are too demure to look or even gander Max is the one who weighs 7lbs 11.2oz.