On a clear day, you can see . . . .

. . .   Maui!  Lanai stands out with its own little white cloud (to the right).  See the ill-defined clouds on the horizon between the two islands?  You can make out the island of Maui as the darker smudge above them.  To the far left, you can distinctly see both the higher northern mountains of Molokai as well as a lower ridge of West Molokai in front.   These clear days don't show up very often. 
Oahu to Molokai - 22 miles
Molokai to Maui - 7.5 miles
Molokai to Lanai (directly south)  - 8 miles