They have very similar meanings. "Death-mark'd love" is pretty self explanatory, and "star-cross'd lovers" are lovers that are fated for doom. This basically foreshadows the fate of Romeo and Juliet and what will likely happen to them due to their forbidden love. Unfortunately I don't have the prologue on me nor did I read it in a very long time, so I can't provide evidence. But that's basically what it is trying to say.
You could look at the point of view that the story is written in.
It should b c that he was wronged by the king
