Beginning a ship manifest search

My great grandfather, Anton Johnson (born Dec 1854), emigrated in 1882 from Norway to Minnesota. His daughter, Casie or Cassie (born Dec 1875) emigrated the same year. I assume they traveled together. My great grandmother, Andrina (or Androna) Johnson, emigrated in 1883 and may have traveled with a son, Ole, age 2. I'm not sure where to start searching for ship manifests. I do not have the name of the ship and I do not know where they came from in Norway. I have found them on several censuses, but don't have any other information. Is it impossible for me to find anything with such limited information? If it's not evident, I'm new to this [:)] Thank you in advance for any tips you can give me.