Are the four brokers entitled to claim a full share of the customary agreed-upon brokerage fee, given that they only connected the buyer to the seller, and what is the ruling on a very large commission that is customarily accepted?

The commission must be known. It is permissible for it to be a percentage of the profit according to the Hanbalis. If the percentage is from a known amount, there is no issue. Otherwise, it is unknown. If the broker's role is limited to connecting the buyer to the seller, it is permissible for him to partner with other brokers, and the profit will be divided among them as they agreed, or equally if they did not stipulate otherwise. However, if the broker undertakes the contract as an agent, his partnership with others is permissible with the permission of his principal. Otherwise, there is a difference of opinion. But merely calling out, displaying, and bringing the customer entails no dispute regarding its permissibility. If the merchant knows and agrees to hand over the commodity to another broker, there is no harm in that. Even if there is no explicit permission, but there is a well-known custom, then custom is like a condition. The company of intermediaries (brokerage) is valid and falls under a business partnership, and the partner is entitled to his share of the profit even if he does not work.