Is it permissible to give a father money from bank interest to get rid of it, knowing that he is not good at managing his money and frequently incurs debt, and is he thereby considered someone upon whom one is not obligated to spend?

It is not permissible to dispose of usurious interest by spending it on one's parents, unless they are poor and the son is unable to provide for them. However, if the father is not in need and has sufficient income, it is not permissible to give him usurious interest, and his mismanagement of spending and finances is not a justification for doing so.