There is nothing wrong with the sun being in the middle, that's not what the "rule of thirds" is all about... (although I suppose you could move it)
Your main subject is not only the sun, but the horizon.........crop out some of the foreground and place the horizon along the lower 1/3 horizontal plane of the frame..
Or in the case of #3, you could have positioned yourself further to the right and brought the palms into the frame along the left vertical 1/3 plane... To fix it, according to this rather flexible rule, you need to again crop the foreground out to bring the horizon to the lower 1/3 horizontal plane, and crop out the vast sky to the right to position the interesting sky colors along the left 1/3 vertical plane...possibly with the outer palm just touching that line..