This tread has gone so crooked I can't bare it anymore.
First:Ao Kiji says something like "how's your grandpa?" Basicly meaning that he thinks the old man is still alive. Ergo Gold Roger can't be their gramps.
Second:"D" may have nothing to do whith the bloodline but more with knowing ancient names. Meaning luffy (and his family) may have some link to "the100 years of blank pages" history.
Third:There's no way of knowing whether Ace or Luffy is stronger Cuz Luffy's unpredictable and Ace is smart. Besides I don't think a fight(read war like with croc') between the two will occur. Ther to much alike.