Well locust.
Vincent - Found in the mansion, downstairs, to get the key you have to find the safe and type this number perfectly (YOU MUST NOT GO PAST ANY NUMBER WRITTEN HERE. IF IT FAILS IT IS PROBABLY BECAUSE YOU ACCIDENTLY WENT PAST THE NUMBER ONCE AND THEN WENT BACK TO IT) "Right 36, Left 10, Right 59, Right 97" make sure you save before hand.
As for Yuffie
Yuffie - Found in random battle in bushes, cant remember what bush. I think next to that abandomed reator.