In the end when they believe Voldemort is back, they used the Imperius Curse on the Ministry to say that they believe

Voldemort back after they use the Imperius Curse on the Ministry to get them to believe that evil Monkies should prevail

after they use the Cruciatius Curse while they gained power for the Imperius Curse.

Later they just got the Ministry to use Voldemort as a cover up for evil Monkies, so they second Imperius Curse was lifted.

And when Dumbledore told Harry about the prophecy he was just planting a story in Harry's mind. Soon after Harry left

Dumbledore muddered, 'Sucker' And then he ran out with his jacket, because at that time he was being played by Tonks.

See? None of this would even had happened if Hermione and Ron didn't start going out.