Does it matter who gets the killing blow? What about in multiplayer? Other player's mercs?

Lets talk single player first:

Say I have a character with 1000 Gold Find.

Say my Merc has 500 Gold Find.

If I get a kill, does the gold drop use 1000 or 1500?

If my merc gets the kill, does the gold drop use 500, 1000 or 1500?

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What happens in multiplayer:

P1 has 1000 Gold Find

P1Merc has 500 Gold Find

P2 has 100 Gold Find

P2Merc has 50 Gold Find.

Players are partied together and in range.

If P1 gets the kill, how much Gold Find is used? 1000? 1500? 1600? 1650?

What about if P1Merc gets the kill? P2? P2Merc?

If P2Merc gets the kill, does it only have 150 Gold Find? Does it have P1 + P2 + P2Merc (1150)? Does P1Merc's Gold Find come into play at all if neither P1 nor P1Merc gets the kill?

It seems like, without factoring in mercs, the Gold Find seems to use the total of all players...I think? If I'm wrong, please clarify!

When it comes to mercs though, I have absolutely no idea how the math works in multiplayer.