Alison - do you know when the chicks hatched? I ran through the thread quickly and I couldn't see anything to be able to gauge how old they are other than the photos ...
Adult peregrines when they feed the chicks are usually pretty egalitarian - and the hungrier a chick is the more it protests which elicits a hardwired response from the parent, so if a chick gets more food a couple of times, inevitably, the other chick will get more food in proportion to how hungry s/he sounds. If a chick isn't getting enough food there is likely something wrong with the chick not that the parents are neglecting or siblings are hogging all the food (though it does look like it often). In all the years I have been banding peregrines, by the time they are banding age, they are in the same kind of condition - if one is a little light, they are all light, if they one is a heffalump, they are all heffalumps. One thing we often forget (us too sometimes) that feedings take place day and night for most pairs and because of lighting for the cameras and/or the fact that we too must sleep sometime, chicks get fed and we don't see it.
Case in point - chick 2 at West Winnipeg right now is still a bit smaller than it's sibling - now at this stage that could be the start of the species' sexual dimorphism showing up in their development or it could just be that s/he is two days younger. S/he however is not getting less food than his/her sibling and the chick looks to be pretty much at the same stage in their development despite the difference in age which at this point starts to mean less and less. Another case in point (two points actually) was everyone's favourite Mistral - she had no problem whatsoever demanding and receiving her portion of any meal after about day two. Her sister Taku was fine up until close to banding age when we notice that one chick was hanging back more during feedings - can't be sure it was Taku or Chinook/Hurricane too full for more - they were Trey's kids so no problem with food availability.
Just some of my thoughts ...