Is it permissible to eat food from an illicit source with relatives, and will supplications be answered in this situation?

It is not unlawful to deal with someone whose lawful wealth is mixed with unlawful wealth, nor is it unlawful to eat from their wealth; however, it is disliked. The Messenger of Allah, peace and blessings be upon him, dealt with Jews and ate from their wealth, which was mixed with usury and unlawful things. As for acquiring items at discounted prices, there is no harm in that as long as it is with the seller's consent. Even if it is without the seller's consent, not all of the wealth becomes unlawful. It is obligatory to avoid the unlawful money itself if it can be distinguished. If it is mixed with lawful money, then not all of it becomes unlawful. You may eat from this mixed food according to the proportion of your lawful wealth.