Rogueleader, I always appreciate you thinking about all the details!

Here is another “argument” with the whole R2 Thing. I think R2 is definitely a more reliable droid… Personally I think he knows when to or not to “talk.” That could be “explained” that R2’S Memory in ROTS was not wiped compared to C3PO (Who is clearly shown in the OT to be a blabbermouth.) My thought at the moment comes from two reasons: 1.) He knows what not to share or not to share as I mentioned (Of course I cannot show exact proof at the moment) but 2.) (better argument) People do not know how to understand astromech droids from their beeps, noises, etc. I say this since the only times astromechs language is understood is through C-3PO or is translated from a ship. (for example in ESB Luke “understands” r2 through the X-Wing since there is a language translator displayed)

So, one COULD argue that R2 either knows NOT to explain or reveal things … or he never “spoke” about what he knows in front of C-3PO so it could be translated. Even if he DOES NOT play the “reliable” role in not “keeping” quite in things, he clearly in Episode IV does not explain or reveal things in front of C3PO and crew.

Lastly, I think I agree again about using the “your mother” over “Obi-Wan” will work. Character wise for Vader it works since CLEARLY Obi-Wan dismisses the “Anikan” in Vader. I think it can be done well with that media you showed. It always Jives well with Vader’s character during that time since he is still “divorcing” himself with Anikan Skywalker at that time. Obviously the more he is with Luke the more that “wall” begins to crumble.