This is from Mugglenets' Deathly Hallows part 1 set report.
You can find it
here.Here's what he says on that subject.
As fans know, shortly before the wedding is when the Seven Potters plan goes into action. Dan had a lot to stay about this scene, which he described as one of the most “daunting” they’ve ever shot.
“It was a highly technical visual effects scene,” he told us. How can he prove it?
“The one shot was 95 takes.” The press gasps.
“Yes, you may well recoil.” The press laughs.
Dan explained for us how the scene technically worked. It was a great description but wouldn’t make sense unless you saw him explaining it with his arm movements. In a nutshell, they used a computer-controlled camera that would film the “exact same shot at the exact same time” over and over again. They used this camera for each of the seven Harry’s in the room so they could make them all appear on screen at once. It took about ten takes for each Harry - hence the 95 takes for the one shot where you see them all standing together.
He enjoyed playing the other characters. “There was no middle ground,” he says while explaining his impersonations, “some are so subtle you’ll have no idea what character it’s supposed to be. Or, so caricatured and exaggerated that you can be in absolutely no doubt which character I’m playing. It’ll be very obvious which one is Mundungus.”
In the Harry Potter books, taking Polyjuice Potion will change the consumer’s voice to the person they are changing into. For the Seven Potters scene in the film, Dan explains, “I think they’re going with my voice [for all the Potters]. I think we established that Polyjuice maybe doesn’t change your voice, although it has in other films, but maybe this batch is weaker.”
He spoke fondly of his work on that scene. “I was delighted by how well I fit into Fleur’s costume.” We laugh and I ask a follow up question. He cuts in, “I’ve GOT to stop saying I look good in girl’s clothes. There are all these rumors already, Jesus.”