Scandinavians were known for using the same names over and over again, which is how they got to be so common. Their tradition was to name the first son after the father's father, the second after the mother's father, and any other sons after the parents' siblings. The daughters received their names following the same pattern: the first daughter would be named after her mother's mother, the second after the father's mother, and so forth. If they had enough children, the couple would begin using non-family names and branch out.
Because of this, it is common for siblings to have children with the same names. Many times there will also be another unrelated family in the area with the same family names, which could become a problem. You can solve this problem by looking at what the witnesses tell you and the clues they provide. First, though, it is important that you know the names of all of the siblings in the family you are trying to distinguish, as well as where they settled.
What you will want to do is follow your ancestor and their siblings through to adulthood when they begin having children. They may not all stay in the same place, so you may have to find them through the census or clerical survey, but you will want to know where they are. The reason for this is that when they begin having children, those children were always christened. The Scandinavians believed that if a child died without christening, their souls would be damned, so they always made sure this was done. For a christening, the parents would choose a woman to carry the child to the baptism, and then some males, usually family members, to witness the event.
The woman who carried the child was usually someone significant, perhaps the person for whom the child was named, the parish priest's wife, or another person the parents held dear.
What you will want to do since the witnesses were usually family members is find the christening records for the siblings' children and look at who was there to witness the event. You will want to compare those names to the ones recorded for children born to the person you believe to be your ancestor and the person who shares the same name.
When you compare, you will usually find that some of the same people will attend more than one christening of nieces and nephews and be recorded as a witnesses, even if they lived miles away. This can help prove which family is rightfully yours.
Which Jens Hansen is yours? The witnesses can tell you.