The correct answers are We still haven't found any friendly aliens. and The crew hasn't finished cleaning the rocket yet.

Still goes before the negative auxiliary verb (still haven't) to emphasize that an expected change hasn't happened.

Yet goes at the end of a negative sentence to show we are waiting for something to finish.

We do not use already in a standard negative sentence like "haven't already reached," and ongoing actions require still, not yet ("is still making").