Is it permissible to take money from an uncle who works in a restaurant that serves forbidden foods and drinks, for the purpose of helping us marry and educate our siblings?

It is not unlawful to benefit from your uncle's money unless you are certain or it is highly probable that it was acquired through a specific unlawful act. However, if there is doubt, it is not unlawful, because the default assumption for a Muslim's wealth is permissibility. The wealth of a restaurant owner who serves permissible foods and drinks is considered mixed wealth, and dealing with someone whose wealth is mixed is not prohibited, according to the more authoritative opinion.