In the case when a yabam marries a widow and has a bechor with her- does that bechor receive the yerusha of the decesased father? or does the yerusha of the deceased father go automatically to the yabam who may do with it as he pleases? That is to say: is the yabam considered like a trust fund and as soon as the bechor is ready, he can gain access to it?
does that bechor get anything from the deceased father? or does his double portion come completely from his biological father?
The Yavam inherits his brother. Although the verse says that the child is "Yakum Al Shem Achiv" he is actually the son of his biological father and inherits him alone. The Gemara learns that the word "Bechor" in the verse "v'Hayah ha'Bechor Asher Teled" actually refers to the Yavam; we learn from the word "Bechor" that it is incumbent on the oldest brother to be Meyabem.