Looking for Decendents of Robert Mauritz Alexander Petterson

Hi. I am new to this game so not sure what I am really doing. Any suggestions and helpful hints would be most welcome. I am looking for any information on the PETTERSON family tree. I am he only daughter of Robin Carl PETTERSON born on 24/08/1937 and am trying to source any info on my grandparents ROBERT MAURITZ ALEXANDER PETTERSON and THELMA ETHEL PETTERSON nee LONGHURST.