All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The answer to your question about the wedding party depends upon the person giving it.
A) If he is a person whose earnings are completely forbidden, then it is forbidden to eat his food or accept his gift.
B) If he is a person whose earnings are mostly forbidden, the jurists have different opinions in such a case. Some jurists dislike eating his food or accepting his gift; others prohibit eating his food or accepting his gift.
We think it is safer to avoid such a case. But, if you mean by your question the forbidden property itself (earned from Riba…), then it is forbidden to eat or accept any food or gift from it.
C) If he is a person whose property is mostly lawful, the jurists also differ on this case, and it is safer to leave it out although such a case is easier than what we stated in point B.
In general, you can respond to his invitation if the food served is not forbidden in itself. In addition, you have to advise such a person and order him in a kind and polite manner to do good and avoid evil.
Allah knows best.