You can fly INTO one city, but return from another. This is called an Open Jaw. Assuming you can find open flights, this should work. Not sure if that is classified as Europe which would mean 50,000 miles vs. 60,000.
check here to reiview miles.
https://www.delta.com/skymiles/use/s...t_us/index.jsp
Yes, make it ONE ticket.
Good luck.