One of the recent previews said that when you're not controlling them, each of the three characters have a set area they'll stick to. But that doesn't mean they'll magnetize to it like magic. Like we discussed in the other topic, it'll probably be possible to encounter the other protags during freeplay simply by finding and driving up to them. R* knows people will try this. So they may even let you interact with them, possibly do the buddy date thing.
Previews have also told us that the map-zoom effect only occurs when the characters are distant. Switching characters should be pretty fast as long as they're close together. However, the game may be stingy about when you're allowed to swap characters. You probably won't be able to when you have a wanted level or when you're on any kind of side-mission or such.
End conclusion: Yeah, you'll probably be able to do something like this. Find Michael, get above him and start falling, then switch to him and watch the body splat. But anything more complicated than that might be too much to hope for.