1. Well, there are no definitive answers for few more things in Ever17 but their are viable explanations.
http://www.kgptzac.info/ever17/d_kickethecan.html - only for 4, 5, 6) i like to think it was programed into Sora (or LeMMIH or whatever controls sound broadcasting) that she should "unconsciously" (if you will) play the sound of can being kicked in 2034 and thus make it consistent with 2017 since there was no Pipi to kick the can this time.
2. Sora in 2034 doesnt know the truth and "real" Sora from 2017 is outside in artificial body. Since you can copy her memory, you most likely can also edit it and delete. IMO, they only programmed the bare minimum, so she doesnt know what is going on - its the most logical thing to do.
Tho, Im not sure what kind of relationship you think about.
3. "Real" names? They are Sara and Hokuto... and if youre talking about family name it would be Komachi since Tsugumi is their mother (and in Japan you take family name from wife, I think... well, It would be Kuranari in case of father anyway)
4. Blick Winkel is you - the player, I mean. There is nothing more to it.