Roy Peter Johnsen

Hello, I am posting here in hopes of some help in building my family tree. My grandfather's name is Roy Peter Johnsen, he was born in the U.S. in 1937. I am trying to find info on his father. He emigrated to the U.S. from Norway in 1921 but after hours and hours of searching the Ellis Island records, Arkivverket records, and using Ancestry.com I was only able to find limited information on him. What I know for sure is after emigrating his name was Egil Johnsen and he married Lilly (Olsen) Johnsen who was also born in Norway. I have found the deed to their house at 1955 East 37th Street, Brooklyn NY. He was born in 1903 and died in 1942, and the deed was past to his wife Lilly. Lilly was born in 1904 and died in 1984, the deed was then past to my grandfather Roy. I found a 1930 U.S. Census that lists this same address and lists Egil Johnson, Lily Johnson, and child Gert Johnson. Also the census spells their last name Johnson, it is a mis-spelling because the deeds and any other info I've found spell it Johnsen. Also I am sure that Lilly is spelt with three L's, not two. (in fact I have named my two year old child after her, Lilly) Information I am unsure of, Roy's daughter (my mom) has told me was that his name was changed after coming to the U.S. Egil is correct for his first name but his last name was Johannesen or Johansen. My mom has some paperwork that belonged to him but only as Egil Johnsen. My mom also told me that Egil and Lilly's first child was named Christian and died from a car accident at age 5. She was unsure of the child's birthplace. Although Lilly and Egil came to the U.S. at different times my mom believed their families ( Olsen and Johannesen/Johansen ) knew each other, perhaps lived in the same area. Well that is about all the info I have, if anyone can provide me with any additional info or where I should continue my search PLEASE PLEASE PLEASE let me know. Thank you very much for your time. Ronald D. Tappen II