i recently just finished the series too.
and after thinking about it and going through 2 threads on the subject this is what i got, though this is just my interpretaion with other mixed in.
[spoiler] kanna is saved and the two kids at the end of 12 are kanna/misuzu and yukito/ryuuya. from what the boy says at the end of ep 12 it implies that he knows whats going to happen to misuzu and yukito which means either he can see into the future O_o.... or he is ryuuya/yukito reincarnate with some memories of what happened. and the whole reincarnate while theyre still alive thing is better explained in the ending of air thread so i wont try to do it here. but its thought that either the crow found away to break the curse or the fact that misuzu died with all those happy memeories and that the happy memories of those other girls (kano etc.) went to kanna and broke the curse.... this thread explains it much better if you read through it.
http://forums.animesuki.com/showthread.php?t=35547