Is it true that you only subtract 1 from the damage of each of your multiple attacks and CAN attack the same figure with all three? And if so are there any penalties to attack value for doing so or anything like that?

There is no modifier to the Sentinels attack due to Multi-Attack. Just subtract 1 to a minimum of 1 damage.

And just FYI - in case you don't already know this - multi-target (more than 1 lightening bolt on a figs dial) and multi-attack (what the sentinels can do) are two different things.

That reduction by one is only for big figs like Sinestro and the Sentinel...You may target as many targets with a ranged attack as you have lightning bolts. Once you have resolved the roll vs. defenses, then you may decide how you would like to distribute damage...you may only divide damage into whole numbers. if doing 3 damage with 2 bolts and hitting both...you can do:
0 and 3
1 and 2
2 and 1
3 and 0

Hope it helps

Ahhh, thanks for clearing things up, I got the two confused. I was very shocked when I read that in shin-goji's data files because I figured that every ranged, multi-targeting piece would be completely rigged

With Multi-target (multiple arrows on a figure) you can not target the same figure. You can target up to the number of lightning bolts on the figure (1-3 typically). Then you divide up the the printed damage to all figures you hit with your roll.

Multi-attack (Sentinel & Sinestro) you can make two seperate attacks, subtracking 1 from the damage of each attack. Apparently Galactus has three multi attacks, but I am not certain how that will work.

Hope this helps HB.

Could you use the two attacks to make two capturing actions?