Is it permissible to distribute the inheritance before the unmarried brother's marriage, and is it obligatory to allocate the costs of his marriage from the inheritance?

The default is to expedite the distribution of the inheritance. It may become obligatory to do so, and delaying it becomes forbidden if one of the adult, mature heirs requests it. There is no difference in this regard between the married and the unmarried. Furthermore, the marriage expenses of the brother do not need to be deducted from the estate before its division.