I think you misunderstood me.
Currently it is so that you
+ can't take Dynaheir and Khalid through (as they die due to SoA story)
+ can immediately recruit Imoen,Minsc,Jaheira (as in normal SoA but with your end BG1 stats)
+ can take any other character through even though (and I guess that's going to be changed) he may appear later in the game causing one character to exist twice (e.g. Xzar or Ajantis). There is another bug that "solves" this problem with Viconia and Edwin as they are missing in SoA and need to be CLUAed in so you won't get two of them if you take e.g. Edwin through and then do the Mae'Var quest (which will be undoable until you spawn Edwin and have two of them again :D ).

If you do that, can you then recruit the second Edwin into your party? Hmmm...PC Sorceror, and two Edwins...

No. The area codes, worldmap file, some of the basic file formats themselves, and probably some other minor stuff is different. It would be possible to write a converter, but that sort of coding is boring and tedious and error-prone, and I dont think anyone is going to volunteer to do it for free.

If you have two installs of BG2, you should be able to. Otherwise you would need the much larger BG:Trilogy mod which allows you to play any section of the game at any time.