I have recently got the death star but my han solo and ben kenobi mini figures have white parts in their eyes (a newer edition of the mini figure) why them and only them.
I don't have the Death Star, and haven't kept up with the latest figure development trends, so I can't be sure about this, but:
Lego frequently updates parts. The new parts are sometimes considered new, and the old parts retired, but often the new parts are considered equivalent to the old parts. Lego then uses these new parts arbitrarily, wherever is most convenient. This leads, sometimes, to a set containing a mix of old and new parts, depending on the sources of those parts during manufacturing. So if, say, they replaced a certain piece with another, nearly identical piece, any set you buy during the transition period could conceivably contain both, if the parts bags in your set came from two different parts of the factory.
If Lego updated the Solo and Kenobi head designs, for use all across the Star Wars line, those head designs may show up in new copies of older sets. Similarly, if there is still stock left of older designs, those designs may also appear in newer sets. When Lego considers the parts to be equivalent, there is no guarantee of which you'll get during the transition.