I'm trying to remove spokes from my wheel and I'm starting by loosening the nipple with a spoke wrench and then use a flathead to unscrew the nipple but on every nipple it will twist loose up until what seems like the last thread so none of the nipples will come off? Is this normal? What do I need to do?

This doesn't make any sense whatsoever. If the nipples can be loosened, then they should come off all the way. It's a simple interface look at it again and see if you can figure it out.

are you doing this one spoke at a time?

because you probably shouldn't... if you're de-lacing your wheel, you might want to equally distribute the slack evenly (ie, top, bottom, left, right, one spot past bottom, one spot past left, one past right, etc).

I got it, you just have to pull somewhat hard on the spoke after you loosen the nipple

You don't need to do this. If you do, you're not unscrewing them all the way. And you are ****ing something up by pulling hard on it.