Hey, Valadius, you have an excellence 5th sense for making The Godfather part 4. Everything you have typed makes perfect sense and is a perfect plot. However, there's just one small thing that I, as well as numerous family members, personally just wouldn't care to see:

If it is possible, not to incorporate any more of Vincento's and Mary's "fling" for each other. I use the word, "fling", because many believe that Vincent's desire for Mary was no more than that. No where in the Godfather 3 did it even make it appear that Vincent was DEEPLY in love with her. "Confused", "horny", "disrespectful", but not "in love". I mean, he didn't say too much when Michael made him the offer of "Mary or Mafia". Mary, on the other hand, could very well have been, because she was young and naive. She, however, displayed her affection more as a childhood crush.

Plus, I think the whole thing with first cousins/any cousins, is just disgusting. I mean, it's just as disgusting as if it was brother/sister.
Then again, it is hollywood, and anything to bring drama to a movie will do just that.
I KNOW THIS IS SUCH AN INSIGNIFICANT POINT I AM MAKING, but weren't you disgusted, too?
I don't know, it's just me venting.......

By the way, send your script into Hollywood, you never know! It sounds like you would do a better job at writting a PASSIONATE storyline for GF4 than the fools in Hollywood!