Answer: The trees you see online or in catalogs are sometimes called fruit cocktail trees. The only problems with these trees are 1) different fruit varieties grow at different rates so without careful pruning, you could end up with a lopsided tree, and 2) as long as the grafted branches remain healthy and not accidentally pruned off during routine maintainence, the trees should perform their tasks of producing lots of different fruits at different times during the growing season.
Your other option is to purchase dwarf or semi-dwarf fruit trees. These trees produce regular sized fruits but they are grafted onto dwarfing root stocks. Many are suitable for container growing and others will mature at about 10' high and wide. I'd recommend checking your local nurseries for these trees rather than putting all your eggs into one basket!
Best wishes with your edible landscape!
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