Andreas(sen)/ (Thuesen) name

My grandfather came from Halden, Norway. His name was Oskar Andreas(sen) Thuesen. His father was Martin Andreas(sen) and may later have changed his name to Thuesen because of the farm that he lived on. Perhaps the 41 Thuesens still in Norway may shed some light on it. I cannot speak nor write Norweign. I appreciate any help in this matter.