How reliable is the information on Ancestry.com. Well on the original of scanned items, that will be as reliable as the people who first entered the event into the original record. As far as the transcribed data such as that from original data, I have found it fairly accurate. If you are talking about Family Trees the answer is not very reliable.at all.
Looking at information early in the topic regarding Halvor Evensen and Gonvor Johnsdatter's children. We have son Svennung born March 1 1845, son John born December 26 1857 and son Helge born November 23 1859.. Can we confirm Helge was a son? There is a record on Family Search indicating Helge was a daughter, christened on 8 January 1860.
Looking at the marriage record of Halvor Evensen and Gonvor Johnsdatter on 20 November 1844, is his father's name written as Even Hansen instead of Even Andersen?