I'd like to see that probability calculation.
-A8
Take Mark 3:31-36 for instance. If it had just mentioned bros, I'd assign a 50/50 chance of them bros, since they could be cousins. Obviously they're not good buddy type bros, or bros as in the fraternity of man, because that's what Jesus says later in response to the announcement about His family outside. Since the announcement is about His Ma and bros, I simply assign an arbitrary value of plus to the 50% value for bros and a minus for the 50% value for cousins. The plus is also warranted by Matt 1:25 and the beginning of John 7. So the probability of Jesus having siblings is 50+% and that they were cousins is 50-%. That's all the quantiifcation that's needed here.