Can I accept a gift or a meal from someone whose income is mixed?
Short answer
This is doubtful. If most of a person's income is lawful, scholars generally allow accepting a gift or meal from them. If you know the item itself came from a haram source, do not take it. If you are unsure, it is better to leave the doubtful, as the Prophet ﷺ taught.
Dan janganlah sebahagian kamu memakan harta sebahagian yang lain di antara kamu dengan jalan yang bathil dan (janganlah) kamu membawa (urusan) harta itu kepada hakim, supaya kamu dapat memakan sebahagian daripada harta benda orang lain itu dengan (jalan berbuat) dosa, padahal kamu mengetahui.
Hadith
Sahih al-Bukhari 52
Narrated An-Nu'man bin Bashir: I heard Allah's Messenger (ﷺ) saying, 'Both legal and illegal things are evident but in between them there are doubtful (suspicious) things and most of the people have no knowledge about them. So whoever saves himself from these suspicious things saves his religion and his honor. And whoever indulges in these suspicious things is like a shepherd who grazes (his animals) near the Hima (private pasture) of someone else and at any moment he is liable to get in it. (O people!) Beware! Every king has a Hima and the Hima of Allah on the earth is His illegal (forbidden) things. Beware! There is a piece of flesh in the body if it becomes good (reformed) the whole body becomes good but if it gets spoilt the whole body gets spoilt and that is the heart
This is general information, not a fatwa. For your own situation, ask a qualified scholar.
Questions about halal and haram
Can I accept a gift or a meal from someone whose income is mixed?
This is doubtful. If most of a person's income is lawful, scholars generally allow accepting a gift or meal from them. If you know the item itself came from a haram source, do not take it. If you are unsure, it is better to leave the doubtful, as the Prophet ﷺ taught.