You can copy keyframes from only one layer at a time. When you paste keyframes into another layer, they appear in the corresponding property in the destination layer. The earliest keyframe appears at the current time, and the other keyframes follow in relative order. The keyframes remain selected after pasting, so you can immediately move them in the destination layer.
You can copy keyframes between layers for the same property (such as Position) or between different properties that use the same type of data.
To paste to the same property of the copied keyframes, select the destination layer.
To paste to a different property, select the destination property.