At the beginning of the Deathly Hallows, a whole team (13 people) comes to Privet Drive to get Harry out of there for the last time.
Pausing only to employ a few of Uncle Vernon’s choicest swear words, he staggered back into the kitchen, clutching his head and staring out of the window into the back garden.
The darkness seemed to be rippling, the air itself quivering. Then, one by one, figures began to pop into sight as their Disillusionment Charms lifted. Dominating the scene was Hagrid, wearing a helmet and goggles and sitting astride an enormous motorbike with a black sidecar attached. All around him other people were dismounting from brooms and, in two cases, skeletal, black winged horses.
(DH, Chapter 4, The seven Potters)
So they came flying brooms, Thestrals, and the giant motorbike, protected by Disillusionment charms.
But the Disillusionment charm is not completely effective, it does not let people become really invisible, just... less visible. (And the motorbike is kind of noisy.)
Harry looked down at his body, or rather, what had been his body, for it didn't look anything like his any more. It was not invisible; it had simply taken on the exact colour and texture of the kitchen unit behind him. He seemed to have become a human chameleon.
(OOTP, Chapter 3, The Advance Guard, just after Moody disillusionned Harry)
How (on their way to Privet Drive's garden) did they went unnoticed through the bunch of Death Eaters that was strolling above the vicinity?
(I can't believe the Death Eaters arrived after the team landed, their info was that the move-out was planned for the nightfall, and they probably were there in advance)