Thanks to everyone for your observations. All are appreciated.
These trees are getting very big. I have to go to the top of my 8'
stepladder to spray them. I hope they don't need to get too much
bigger to satisfy Mother Nature. I will consider some summer pruning.
My other tree, the one that is so prolific, began producing after only
a couple of years, and is the same variety as the ones we're talking
about. I have fertilized it with fruit spikes, but nothing more, and
not regularly. They certainly may need some. I was thinking more along
the lines of not encouraging green growth, but neglected to consider
fertilizing to encourage blossoms.
As far as the pruning, I've done it primarily for shaping the trees
early, and to keep them from getting too big. Even so, I try not to
take more than a third of the new growth, which shouldn't be too much.
I'm afraid if I don't do any pruning, I'll need an extension ladder to
spray and harvest fruit, assuming I ever get any. My partner has
observed that my technique for pruning may not be the best, but I argue
that the other tree is well shaped, produces abundant, healthy fruit,
so my work can't be that bad. It may be that these are just going to
take longer to produce.

Thanks again, I'll try to put all of the advice to use.
Bill