Emil & Theodore Pedersen Braaten

You have been very helpful on questions that I have asked in the past and was hoping you could lead me in the right direction for this question. I have a 1875 Census found on Familysearch.org. https://familysearch.org/pal:/MM9.1.1/X7N3-344 These are some of my husbands ancestors. We know that Thorsten and Lisabet are the parents of Thorsten, Krsitane and Thea (as well as a few others). What seems to be confusing is who is the mother and or father of Emil and Theodor? I was just assuming that they were the children of Thea and that Thea may or may not have been married in the past. Then she came to live with her parents bringing the boys assuming HER father's name and giving it to her boys. Is there any place to find birth records? or are those some of the missing years? Thanks.