Not Enough Sleep

The girls don't get enough sleep.  I've been keeping track and about half the time they get less than 11 hours per day and the rest of the time they get a little more than 11, but definitely less than 12.  They should (according to Babycenter) be getting between 11 and 14 (so, half the time they barely get the minimum).  This has been the case for  last 9+ months, when they dropped their nap at exactly 2.5 years of age.  For the most part they seem to do fine on this amount, occasionally falling asleep in the car or less often on the couch in the late afternoon/early evening.  But lately they seem to almost always get really cranky and fussy in the late afternoon/early evening.  Then they get super wound up right before bed, which I've read is actually a sign of overtiredness.  So I'm trying to figure out how I can get them to sleep more.  I can't put them to bed earlier, because they simply won't stay in bed, let alone go to sleep.  We have a hard enough time getting them to bed between 9:00 and 9:30.  Any earlier is downright impossible.  It seems logical that if I started getting them up earlier in the morning that they would in turn go to bed earlier, but first of all, that only solves the issue of them staying up "too late", not of getting more sleep, as they would still only get 10-11 hours, they'd just be on an earlier schedule.  Second of all, it wouldn't work anyway, because more often than not they would just fall asleep in the late afternoon/early evening and still stay up late.  Sigh.