If I hit the trigger to make my cure hit all four members, it still costs the same MP right? What % does each member get? Is it the same when casting Fire on a group of enemies?

If you have two party members, they each get 50%. Three party members get 33% each. And four get 25% each. It's the same sort of breakdown for enemies as well. I think that's how it goes.

You are correct Swedish. A text-book answer...props to you! ^_^

I am not entirely sure that it's the same if you're casting an offensive spell. I think it's varies depending on the enemy's level. I could be wrong.

almost 100% sure that is wrong.

I cast cure on 1 target it heals for like 500-550ish (guess) or w/e I cast it on 4 it hits each for 200-250ish.

I know 500 isnt that acurate but I know for sure that I've never had a cure hit over 700 (250 x 4) = 1000. (heck even 200 x 4) = 800, so this is definately not the way it works.

I think it is more like:
1 target: 100%
2 target: 66%
3 target: 50%
4 target: 33%