My condolences to you on your loss, and on the extra trauma which your family is going through as a result of your mother's actions and your father's reaction. Unfortunately, I do not believe that it is illegal to send cremated remains to another person, as they aren't considered a harmful or hazardous substance. I don't believe that the motive is really important. However, you and your brother need to sit your father down and make him understand that, while your mother may not have been a perfect person, she was still your mother and you will be hurt and dismayed by his actions if he does what he is planning to do. If that fails, perhaps you can take the ashes, or portions of them, so that you will at least have something left of your mother which you can deal with in ways you feel are more appropriate.