Well, at least you don't have to take the blame for this goof-up; the original owners get the prize for not investigating what roots needed to survive.
Please read this previous Smarty Plants question which deals with tree roots under foundations or concrete. It can't possibly be good for the tree or the patio to have the situation you describe. You can't ensure the trees stay safe, although if they are vigorous enough and the roots go out far enough to where the gas exchanges and moisture access are better. Line of least resistance, you can always let what happens happen. Either the tree roots will break through the concrete, thus ruining the patio, or the trees will begin to suffer, and ultimately die.
The pear is native to coastal and mildly temperate regions of the Old World, from western Europe and north Africa east right across Asia. Since at the Lady Bird Johnson Wildflower Center we recommend only plants native to North America as well as to the area in which they are being grown (in this case, Tarrant County), we don't know much about the cultivation of the pear, but we can bet it's pretty close to that of other trees, native or not.
Your tree may very well be a Bradford Pear, which has been somewhat overused as an ornamental in recent years. If you follow the link above, you will learn they don't live very long anyway. Perhaps that will help you make your decision.
