I think I might have found some info on John and Nicholai's parents. I believe they are Gabriel Olsen and Elen Marie Hansdatter. Nicolai Marthin Gabrielsen was christened 05 JUL 1835 Tromso, Troms. Johan Elias Gabrielsen was born 15 Nov 1825. I don't have any birth or marriage info on the parents yet.
I haven't found if they have any other siblings. If you use these names, you can find them on www.familysearch.org
You mentioned in one of your earlier posts that nicolai's family started using just the "gabriel" surname. Mine did too beginning with John's son Hans who died in 1940.
I'd be interested in getting a list of Nicolai's children and descendents (as much as your comfortable with giving). My information on that side of the family is pretty sparse. I can supply you with what I know about John Gabrielson's side (I'm a 2g grandson of John's son Hans).