Obi wan is never on tatoonine in episode 2 and he never meets shim skywalker, so how does he know who they are?
shareA little research maybe. He knew Anakin lived in Tatooine and went back there to find his mother. Not hard to question a few locals to find out if Anakin had any extended family there.
shareAnakin most likely told him offscreen between Episode II and III.
shareObi Wan had a secret affair with Owen. That's why he knew him.
I'm just on my way up to Clavius.
A bigger mystery is why the Jedis think leaving Luke with Beru and Owen is a good way to hide him. Darth would discover Luke the first time he came home for Christmas (er, I mean, Life Day).
shareIf Anakin ever did want to step foot back on the planet he hated with such a passion why would he think Luke is not Owen and Berus kid? Just because?
shareYeah, but it would probably set off vader suspicions if he came to find that Luke is not an Owen but a Shywalker.
shareYeah, I can see it
Owen: Hey Anakin, how you feelin?
Vader: That name no longer has any meaning to me
Vader: ...Is that a kid? He cant be yours
Owen: Yeah, uh he is...
Vader: Oh really? Whats his last name then?
Owen: Skywalker- *beep* I mean Lars!
Vader: All too easy
Boom shywalker not Owen, rebellion over
Also, once Luke is talking, he'd be calling them "Uncle" and "Aunt," as we know from Ep. IV. I guess Owen would then claim that Luke is the child of Beru's dead sister.
Your mini-script made me chuckle. Good job.
The real question is why would Owen and Beru tell Luke that he is their nephew and not their son
But to your point if Vader was ever going to go back it would of happened right after 3p when Luke was still a baby and not talking. Doubt he would wait for the 10 year reunion of slaughtering younglings to go visit his relatives. Also thats assuming Luke wouldn't be too scared to talk when Vader sits down for dinner
What do the slaughtered children on corascant have to do with visiting relatives on Tatooine. Perhaps he has a taste for the blue milk or to visit his mothers grave. I doubt the Lars are aware of the little incident in the Jedi temple and he could very well lie about how he came to being in the suit and not to believe what people say occurred between him and obi wan.
shareLuke would be with family...that doesn't make live under the stairs, and we know from I & II that Vader would never even consider going back
"Few people understand the psychology of dealing with a highway traffic cop."
Darth would discover Luke the first time he came home for Christmas (er, I mean, Life Day).
I think it's probably reasonable to assume that Anakin told Obi-Wan about everything on Tatooine, well, maybe not all of it directly, but Anakin is sort of known for having a weak mental defense in the Force (i.e. his thoughts are fairly clear for all to see), and Obi-Wan would have known whether Anakin told him or not.
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Because he read the script. He, Obi-Wan, what's that there next to you on the ground after you beat Grievous? Is that the script?! 
shareBecause he read the script. Brilliant.
Padme could have told him when he visited her.
She would have been more likely to give him more information than Anakin.
Since when is a family your mother married into considered your "relatives" ?
Better three hours too soon than a minute too late.- William Shakespeare
It would have worked better if Anakin had never met Owen & Beru that way... just the fact that Obi-Wan brings Luke to Owen & Beru puts Luke's life in immediate danger.
There was no telling if Darth Vader would come back to Tatooine and confront Owen & Beru again regarding the fate of Shmi, in Episode II I could tell a great resentment coming from Anakin regarding the Lars family that they had abandoned Shmi to the sand people, to the point where Anakin wanted to kill Cliegg "yarr I'm a pirate" Lars, as well as Owen & Beru.
Why wouldn't Obi-Wan just hide Luke on any number of out rim worlds not associated or linked with Anakin Skywalker or Emperor Palpatine.