We appear perplexed... There are "Biannual baring" apple varieties; but not "in harmony" with their neighbors! I've heard of Squirrels eating blossoms before they open; and if there were only a few young trees, a squirrel could easily have gotten to (almost) all of them! Late - "hard frosts" will damage "set" fruit blossoms, but not eliminate the flower itself (at least here in Oregon). Too much nitrogen fertilizer tends to cause excessive vegetative growth - too the detriment of "fruit buds." But with several varieties, fruit Spurs vs. Tip-bearers, that shouldn't account for your near total loss?
I'd lean toward the varmint!
Have you seen any Squirrel action
in the vicinity? Squirrel-guards around the tree trunks? But far from definitive - I'll leave this open to the wiser among us.
As for this seasons lack of crop - lets let them put their collective energy into healthy growth and more blossoms than you can shake a stick at next Spring