The problem is a little vague, particularly at the point of "tried cut and paste." In Eagle, you actually cut and paste, not copy and paste.
1) Set up new (blank) screens for the new part. Eventually, you will need 3: symbol, package, and device. I generally set them all up at once; then, move to cut and paste. (That assumes the package is not a standard package.)
2) On the existing part, highlight the area, select the cut (scissor) tool, and right click to "cut."
3) Then go back to the blank screen and paste X2.
John
Edit: You are in edit library mode, right?