in the movie breaking dawn part 2 alice shows aro what would happen if they fight. but she cant see the lobos and she showed jacob and renesmee and leah and seth. why?

This is what Stephenie dicho about it in an interview

"Are there a few little trespasses against the mythology in this vision? Yes, as some of tu have pointed out. The consensus was that a minor deviation from what had been established was forgivable in the name of entertainment. I had a few very elaborate solutions, but they were too confusing and not nearly as cinematic as the final product. And obviously, the result was very entertaining."