Is taking money or gifts from a person who relies entirely for his livelihood on a father who deals in drugs considered unlawful?

It is not permissible to deal with your colleague's father by taking a gift or a loan if all his earnings are from unlawful trade. However, if his money is mixed and he has other sources of income, then taking from his money is not prohibited but disliked, and the dislike increases with the increase of unlawful money within it. He should be advised to cease his actions.