Does a living brother fulfill his own pru ur'vu during a Yibum marriage?
If a man is required to father a boy and a girl (according to B"Hillel in Yevamos 61b), but is married to his late brother's wife (the brother died, childless) then do (all) the children who are born of the Levirate marriage belong to the dead brother's "line" and fulfill the dead brother's or do they (some or all?) conclude the living brother's obligation?
As wikipedia puts it, "The offspring of the levirate union would be seen as a perpetuation of the deceased brother's name." The children (according to the same wiki page) might even inherit from the dead brother so they are considered "his" in certain ways. Would the living brother need to divorce this wife and marry another so that he can have children outside the context of his brother's marriage?