Well here are a couple of suggestions. First, I would make a drawing with the dimensions of your backyard and try some different ideas on how to best use the space. It’s easier to plan and correct mistakes on paper rather than when the trees are in the ground.
If your wanting to do a 2 dimensional tree- espalier will work or you could just prune/ train a spindle so the branches are in a single vertical plane. It’s sort of a simpler espalier. A informal fan type espalier will also be simpler than a formal espalier and less work.
I would look at these two threads they have useful information on laying out an orchard with limited space.
The tree spacing calculator in the threads is very good at determining spacing since it takes into account soil, rootstock, scion, irrigation, and training style.