Thanks for the suggestions, especially about the positive vs. negative
reinforcement.

Generally I've just tried to the keep a distance between the cats. Since the
new one (former stray) follows me around, that's usually not too hard to do.
The cats being free to go in and out of the house, which is wide open, the
only way I can really separate them is to close the new one in a room, or in
the house as a whole while I go outside.

The feeding ritual (though they always have two kinds of dry food available
all the time) is to go outside at feeding time and round them up, by walking
around to all of their usual places and calling them. When they are coming
I go back in the kitchen and fix their plates and bring them out to them.
Usually this goes well, because I feed the new one at a little distance from
the others, and make sure he doesn't move in their direction. But sometimes
something really distressing will happen, like one of them coming when I call,
but then seeing the new cat nearby, and turning around and deciding to skip
the meal. So the next time I make sure that doesn't happen by closing
the new one in the house while I round up the others and feed them. Even
though the new one is being fed too, he still cries while I'm outside with
the others, and they can hear him.

We go through similar problems when it rains and one of them won't come to
shelter if he catches sight of the new one.

Though I can't help but like the new one for his following me around and for
his affection, he has ruined all of the delicate rituals that I had going
with the other two males. My relationship with the older female is nearly
back to normal, because she has not been spooked by the new one ever since he
stopped marking territory, but she never gets in my lap anymore, something
she used to do often.

The main reason all this happened is because my house always has ways for the
cats to go in and out at will, even in the winter, so I invited the trouble,
which is a continuing soap opera.

Calvin Rice