DB Multiverse

About the characters in space.
Although they keep their mouth open, I can assure you that Vegetto and Buu are only talking by telepathy.
Vegetto is holding his breath. Buu does not need to.
There is no gravity. No "down". If Vegetto and Buu are... parallel, it's because Vegetto teleported himself in order to face him.

It was said that "Freeza could survive in space", meaning that Goku would die in space, so what about Vegetto?
In fact, you, and a Saiyan, can't survive in space because you need to breath, because you take death rays in your head (usually stopped by the Earth's atmosphere), because of the lack of pressure (your body exploding like a potato chips bag you take with you in the mountains), because it's damn cold.
A human would die in like 30 seconds. But we're weak. I'm quite sure Vegetto can resist these problems for several minutes.

About relative speed : why are Vegetto and Buu always near Broly, who is pushed at high speed by the attack? Because they are in space. They got the same speed.
With no gravity to drag you, no air to stop you, when you're going at a speed, you're keeping this speed, with no effort.
How did they gain this speed? Well, think of that, Goku's on Earth, standing still, but moving very fast around the sun, ok? Namek is rotating around its own suns. So Namek and the Earth are, far away one from another, moving at huge different speeds. When Goku teleports on Namek, he adapts instantly his speed to the teleportation point so that Namek don't go without him. Vegetto and Buu adapted their speed to Broly instantly when teleporting near him.

As for Broly, he is so Legendary-ed, that he is still transformed (and unhurt), but prisoner of the attack.

And for sound in space ("zip" for teleports), it's only heard by the one making it. Think about "Star Wars" :)