Looking for family of Edvardsson or Karlsson

[Kerstin Erickson]

My name is Kerstin Erickson. My father, Sture Knut Valter Edvardsson, and I are searching for information on his grandparents. We have very little information to start with. I hope someone can help.
 
My father was born in Stockholm in 1951. His father was Rune Knut Edvardsson who married Brita Evior Linnea Fredericksson.( She was born in 1921 to Valter Fredericksson and Elsa.)Rune Knut was born to Knut Arvid Karlsson.  
 
This is where I have a problem. Knut Arvid was born with the last name of Karlsson and according to my Farmor was later adopted by his mother's second husband, giving him the last name of Edvardsson.  
 
Thank you in advance to anyone who can possibly help me.

[Jan Jutefors]

Kerstin,
 
I have sent you an answer at your email, because there was someone maybe still alive, and I will not put that persons name here.
 
Best wishes