Is it permissible for one of those offering a sacrifice to share less than one-seventh in a cow, and does that affect the rest of the participants in the sacrifice?

It is permissible for seven people to share in a cow or a camel for the purpose of sacrifice (Udhiyah (definition)), provided that the share of the sacrificer is not less than one-seventh. As for someone who desires the meat and not the sacrifice, it is permissible for him to participate with any amount. If one of the sacrificers contributes less than one-seventh, his sacrifice is invalid, but this does not affect the validity of the sacrifice of the other participants.