Is it permissible to accept money from a father who earns his livelihood from gambling, knowing that the assistance often exceeds what is needed?

If your father has no source of livelihood or money other than gambling, then his money is unlawful and impure. You are not permitted to benefit from it as long as you are not in dire need of it. You must advise him to abandon this forbidden act and the consumption of ill-gotten gains, for consuming unlawful money has severe consequences, including being deprived of having prayers answered, as stated in the Hadith: "His food is unlawful, his drink is unlawful, and he is nourished by what is unlawful; how then can his prayer be answered?"