Answer: These trees usually mature to about fifteen feet tall and wide. Planted at about eleven feet apart they should eventually blend together at the tips and create a lovely effect. I hope there is enough width between the houses for the branches to spread out.
For a cohesive look and to tie the trees into the rest of your landscape you might consider using a total of five of the same tree, with two more along the neighbor side of the patio, and two more placed out past the end of the patio in the lawn area to make an approximate triangle with the tree at the corner of the patio. By that I mean not continuing the straight line of the three on the side of the patio by the neighbor, and not in a straight line along the back of the patio forming a ninety degree angle, but somewhat unevenly but pleasingly spaced into the surrounding area.
At the corner of the patio where the trees are you might add a few, say three or five or seven flowering shrubs such as rhododendrons to soften the overall look of the corner and back of the patio; you could also use a groundcover beneath the maples to tie them together visually and also help keep the roots shaded.
I hope this helps.
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