It sounds like the trees
are not being adequately pollinated. When the blossoms bloom, see if there are lots of bees and things collecting pollen. Honeybee populations have been devestated in recent years.
It could also be that there was an apple tree
nearby that were chopped down or died, which once provided superior pollination. If all the trees
your friend has are of one or two varieties, they may not be getting the type of pollination they need...some apples are picky about this.
Other issues...freezes, drought...could be to blame, though.