20 years ago it was scripted that they were brothers. Then Lucas realized how dumb that was and made Owen Anakin's stepbrother. There is now no connection between Owen and Obi-Wan.
Owen IS NOT Obi-Wan's brother. That's stupid. Owen is Anakin's step-brother. As for everything Obi-Wan tells Luke about his family in ANH, it's all lies.
If he ain't in the mask, he ain't Darth Vader, besides no one living knew his sith name. Maybe you fell asleep watching the movie, but Anakin becomes Darth Vader long before the suit.