Can someons parents have sickle cell anemia and then they don't get the trait nor the anemia?

Another possibility. One sickle cell syndrome is a combination of sickle cell trait and beta thalassemia. The symptoms are most like sickle cell disease. If this person had children, they could pass on the beta thalassemia and not the sickle cell. Otherwise, people sickle cell disease will have children with either trait or disease.
No. If 1 parent has sickle cell anemia, the children will all have trait. If both parents have trait, or if 1 has trait and 1 has sickle cell anemia, the children can have trait or sickle cell anemia. If both parents have trait, children can have normal hemoglobin, trait, or sickle cell anemia. And, finally, if both parents have sickle cell anemia, all the children will have sickle cell anemia.