Praise be to Allah.
It is permissible for seven people to share in the udhiyah, if it is a camel or a cow, because of the report narrated by Muslim (1318) from Jaabir ibn ‘Abdullah (may Allah be pleased with him) who said: We offered the sacrifice with the Messenger of Allah (blessings and peace of Allah be upon him) in the year of al-Hudaybiyah, a camel on behalf of seven and a cow on behalf of seven.
Ibn Qudaamah (may Allah have mercy on him) said: It is permissible for seven people to share in a camel or a cow, whether the sacrifice is obligatory or voluntary, and whether all of them want to offer a sacrifice, or some of them want to do so and the others just want the meat.
End quote from al-Mughni (3/296)
For more information, please see the answer to question no. 45757
The share of each of those who join together, if they are seven, is one seventh of that udhiyah. It does not affect the partners in that case if one of the partners shared in that udhiyah with them using haraam wealth, if they were not aware of that, because each of them is responsible for his own efforts and actions, and no bearer of burdens will bear the burden of another.
But if the partners were aware of the situation then they should not help him in disposing of his haraam wealth and benefitting from it. Rather what they should do is denounce him for that, and it is prescribed for them to shun him so as to deter him from his sin and from consuming haraam wealth.
Finally, we appreciate your praise for our website, and we ask Allah to help us and you to obey Him, and to make us among those who call to good. We are very happy to hear that you tell people about the website so that they can benefit from it. Muslim (2674) narrated from Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (blessings and peace of Allah be upon him) said: “Whoever calls others to guidance will have a reward like that of those who follow it, without that detracting from their reward in the slightest. And whoever calls others to misguidance will have a burden of sin like that of those who follow it, without it detracting from their burden in the slightest.”.
And Allah knows best.