All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
If the person knows that the marriage banquet will lead to a forbidden matter then it is an obligation to avoid this for two reasons:
1- The marriage banquet is not an obligation according to the most preponderant opinion of the scholars but it is a desirable Sunnah.
2- Preparing a marriage banquet and inviting people to it is a benefit, and evil is harm, and repelling harms comes in priority over achieving benefits.
Nonetheless, a Muslim should be strong on the truth, so if you are the person who want to prepare the marriage banquet, you may achieve two benefits: you may prepare the marriage banquet but you should not allow any one whose presence would lead to a prohibition, whoever that might be. If you do so, you might encourage those who want to do the same thing like you, to follow your example and do what you did. Therefore, you will get the reward of someone who revived a Sunnah (recommended act) or destroyed an innovation, and you will get the reward of those who were affected directly or indirectly by your act and did it, until the Day of Judgment. However, if you are unable to control the matter according to the religious requirements, then it might be better for you to slaughter a sheep and invite the noble and righteous people whom you know while having the intention for the marriage banquet. Then you may distribute whatever remains of it to the poor, the relatives and the neighbours, and announce to them that this is the food of the marriage banquet.
Allaah Knows best.