Are you talking about multi-graft fruit trees? Mother Nature doesn't have the same attitude about diversity that humans do; she prefers competitive dominion. Generally one variety of scion wood grows much better than the other three and finally takes over the whole tree. Maintaining a more equal balance would be a constant pruning chore. You can plant individual fruit trees quite close together, so the supposed spacing-savings of the 4-in-1 trees is questionable. Most people who've had good luck with multi-grafts have done their own grafting.

What is said above I've found is true with all of my multi-graft trees.

I have directions for the planting of several small trees in one hole, but can't open the file on this new Mac. :-(

As I recall it was basically finding the trees you want -- 3 or 4;

dig a large hole with a large mound in the middle;

arrange all trees around the mound so their main trunks are only a few inches apart OR are just touching depending on which directions you might use; AND the trees will be planted no deeper than they were before;

back fill;

prune all branches so that:
1. none are going into the new trunk area;
2. none are crossing or getting in the way of another tree's branches;
3. there is good shape to the whole arrangement;

finally.... continue to maintain this pruning method.

Also, I seem to recall that proper fertilization is of the utmost importance since you will have multiple trees competing for the same nutrients.

I like my 4in1 peach tree. There is one branch that is twice as large as another. One branch never really took off. The fourth branch broke off because I let it bear too many peaches the first year.
Ruth