It is not best to have all one kind of tree togeather.
Insects go from one to the next with ease. By mixing
varieties there is at least some barrier to this.
You're making it at least it little more difficult
for the insects and disease to get everything.

Remember some will need a little more room.

In terms of pollination, it's such a small area it doesn't matter much where you plant your trees. Peaches, with a few rare exceptions, don't need a pollenizer. Still, I would put apples by apples and peaches by peaches. Reason is, your trees will need some form of pest control (spraying). Makes it lot's easier spraying trees of the same kind together (Don't have as much overspray issues, etc.) Although it's a clever thought, keeping like kinds of trees separated will not help with the major pests. They're flyer's and will easily go from one tree to another in a 1/4 acre planting.