apple and pear don't hybridize. They don't even can be grafted one in the other. The tissues are rejected. There are round species of pears naturally shaped as an apple but they are not "pears" (common pears) neither apples. Are from Japan and are called nashis or sand pears. Tasty and crunchy, very good in salads

Pear and quince can hybridize producing a fruit called Pyronia (= Pyrus x Cydonia). Is not better than any of the parents, so it remains basically unknown and unavailable.