I am not a fan of 4 in 1 fruit trees, to begin with, so would not select one for an espalier. Just looks like too many problems dealing with such a variety in a confined space. Al

I have grown successful and very fruitful espalier fences in Seattle and San Jose using multi-grafted apple trees. The husband does not like pears and we only do apples. These are trees grafted specially for espalier- they are already in the flat form. I would rather go for the Dutch fence with different varieties but again, the husband is charmed by the grafted trees.
PP

I would enjoy seeing pictures of your espalier efforts. I have 2 semidwarf Asian pears being trained against a 6 foot wrought iron fence in full sun. The branches are simply being trained horizontally. I like the effect.

I didn't try a multigrafted tree because they're a bit more expensive, and being a beginner, I feared breaking a precious branch and losing that particular variety.