so i went to google and got some conclusions for this, ending is an open one, and these are the mysteries with some speculated answers:
is johan alive or dead? no one knows, maybe hes alive and got out of the hospital again, maybe hes dead, and if hes dead, was it because tenma couldnt save him cuz the condition was poor, the wound was so severe, or did he not save him on purpose(quite unlikely as tenma still believes that all lives are equal and couldnt shoot johan to begin with)? some argue that cuz the room johan was in was lacking in security guards and life support system even tho he was such an important character who was behind all the murders, all of this is inside tenma's head cuz he couldnt save johan the 2nd time, but there was still signs of someone lying on the bed, which if wasnt johan would be kinda weird.
what is his and his sister's name? we just dont know
why did the mother dressed them up? probably cuz she was experimented on and she wanted to disguise them to escape or something
who was the unwanted one? dunno
in the end, the only thing i can think of is urasawa is such a wonderful mangaka