Is the surplus money that devolved to the Hasabi Council by force after the father's death considered usury, and is it permissible to use this money for marriage or building a family home?

The ruling on surplus money depends on its source. If its source is a prohibited investment like usury (riba), then it is forbidden and must be disposed of, unless you are poor and wish to marry but do not possess the means for it, in which case it is permissible for you to take from it according to your need. However, if its source is a donation or a permissible mudaraba (profit-sharing) contract, then it is lawful.