What should the questioner do regarding his father's money, which he discovered to be from bribery? Should he complete his marriage with this money? Is it permissible to give charity from it? Is there an expiation for his father?

What your father was doing, taking money in exchange for tax reduction, is not permissible Islamically. It is a forbidden bribe. Therefore, you should advise him to repent and to rid himself of an amount equivalent to what he took in bribes. As for your benefiting from his money or marrying with it, there is no issue if he gives it to you, because his wealth is mixed, and the preponderant opinion is that it is permissible to benefit from his money with his permission and to accept his gift.