What is the ruling of the Shari'ah on a partner joining one of four brothers in his share of an Eid sacrifice, specifically a cow, and is this sacrifice sufficient, and does the partner receive the reward for the slaughter?

It is permissible for seven people to share in a camel or a cow, and this is the view of most scholars. However, it is not permissible for one of you to share half of his portion with another person, because the share of each of them would then be one-eighth of the cow, and this is not sufficient for an Udhiyah (sacrifice). Rather, they would receive the reward for the price of the aforementioned meat.