The mechanics of fraternal polyandry are simple. Two, three, four, or more brothers jointly take a wife, who leaves her home to come and live with them. Traditionally, marriage was arranged by parents, with children, particularly females, having little or no say. This is changing somewhat nowadays, but it is still unusual for children to matry without their parents' consent. Marriage ceremonies vary by income and region and range from all the brothers sitting together as grooms to only the eldest one formally doing so. The age of the brothers plays an important role in determining this: very young brothers almost never participate in actual marriage ceremonies' although they typically join the marriage when they reach their midteens'This has been an excerpt from Professor Goldstein's paper. Read the whole thing here.
The eldest brother is normally dominant in terms of authority, that is, in managing the household, but all the brothers share the work and participate as sexual partners. Tibetan males and females do not find the sexual aspect of sharing a spouse the least bit unusual, repulsive, or scandalous, and the norm is for the wife to treat all the brothers the same.
Offspring are treated sirnilarly. There is no attempt to link children biologically to particular brothers, and a brother shows no favoritism toward his child even if he knows he is the real father because, for example, his other brothers were away at the time the wife became pregnant. The children, in turn, consider all of the brothers as their fathers and treat them equally' even if they also know who is their real father. In some regions children use the term "father" for the eldest brother and "father's brother" for the others, while in other areas they call all the In such cases, all the children stayed in the main household with the remaining brother(s), even if the departing brother was known to be the real father of one or more of the children'brothers by one term, modifying this by the use of "elder" and "younger."
Goldstein, Melvyn C. "When Brothers Share a Wife". Posted: September 11, 2009. Available online: http://anthropologyman.com/files/15_When_Brothers_Share_a_Wife.pdf [Natural History. 96(3):109-112, 1987.]