I've heard that if you've had 2 c-sections, you can't go through a normal delivery for your 3rd baby. Is this true?

Yes like what Samantha said there is a choice but depending on whether you want to take the risk. Of course there have been successful cases but it's really easier to tear given the vigorous stretching when baby is about to be born. For myself I probably wouldn't take the risk. Oh, and you'll need to spread out the pregnancy for the wound to heal thoroughly before you are able to give birth again.