S=splashed figs
T=targeted fig
x=empty square
A=attacker

xxxxxx
xSSxxx
xxTxxx
xSxxxx
xxxxxA

The roll hits all defenses and it's doubles. Do all the figs who take damage suffer knockback? Thanks in advance.

Yes, unless they have powers that prevent/ignore knock back.

IIRC, the order of events goes like this:

T takes knockback. Since the line is not perfect, he can move to, say, the left. Then each S target takes knockback from where T was sitting.

that's what I believe to be correct. It sure is great to split up a bunch of defenders!!

Actually what happens is that the figures farthest away from your attacker would take the knockback first, then the next closest, etc.

So in your example, all the S guys would be knocked back away first (since they're 3 spaces away from A), then T would be knocked back away (as he's 2 spaces away from A).

This is per the General Errata and Clarifications, page 4:

Esper3k is right. It's the farthest back first.... basically to simulate everyone being thrown back at the same time (which is not an option in this game), so the farthest ones back get KB first so none of them knock into each other (which wouldn't happen if they were really all knocked back)