1,2,3) Yes.
4) Yet another ancient picture dug up:
http://img19.imageshack.us/img19/5391/conj3.pngIt still bears the name "conjecture three", but now it's a certain thing - reverse engineered from the exe. And again, roughly speaking, this happens:
a) take about 1/6 bullets, let each of them try to hit the primary target independently,
b) push those that missed along the central path, trying to hit other targets on the way, skipping the primary target (they had their chance to hit it already),
c) push another 1/6 of the bullets along the central path, each time the volley encounter a critter, bullets will try to hit it until one of them fails, the rest will not try to hit it and fly to the next target on the line (if any),
d) push 1/3 of the bullets in the same manner as in c) along the left line,
e) push 1/3 of the bullets in the same manner as in c) along the right line.
"Left line" consist of the hex adjacent to the attacker (it's common for all paths), then it jumps to that one hex which is 3 hexes far from the attacker, and continue along the drawn line. Same for right path. They can get pretty weird looking if the central one is not "straight" hex-line. In FOnline they are just the best approximations of "real" lines drawn through the centres of the attacker's and the target's hexes, and their parallel translations. In FO2 they produce similar results, but are slightly bugged and inconsistent.
About the "acidental" shooting of the close target - yes. That's actually how you could effectively use a minigun in FO2 to maximize your kills - killing one far target with 1/6 bullets, and three more standing close on the main lines.
Note that in FOnline, for AI purposes, such "accidental" attack usually counts as a normal attack - in case of players it's impossible to tell if this was a deliberate action, or true accidental fire. Such attack is not treated as intentional only if the attacker is a non-follower NPC (obviously no problem with that, as it is fully controlled by the server).