When can they come home?

There's no hard and fast rule.  Apparently, at various points in the past NICUs had benchmarks like "five pounds" or "full-term birthdate."  We have been told neither.  Instead, it's all about whether the girls are able to behave like full term babies in the most important respect -- by never ceasing their core respiratory and circulatory functioning even during their most demanding activity (nursing).  We don't know when that will happen, but we know it's as much a function of the normal progressive development of the autonomic nervous system during gestation as it is a matter of training.  Expecting the girls to maintain perfect balance amongst respiratory and circulatory functions at 33-34 weeks of gestational age is a bit like expecting a ten year old to drive a car -- there are a lot of aspects of the task that are within the kid's grasp at any given moment, but you can't trust that developmentally he or she is ready for every circumstance that could be presented.

So we'll wait for a green light from the MDs.  It's frustrating to see them doing so well and still know that it will be a while before they can go home.