Are the funds received by the brokers permissible or impermissible in the aforementioned land sale, and is it a condition that the owner of the land and the buyer know about this? And if the funds were impermissible, what is their fate?

The issue with intermediaries in land sales boils down to two possibilities: Either the landowner has explicitly or implicitly authorized them, in which case there is no blame on them for taking an increment over the specified price. The second possibility is that the seller has authorized only the first intermediary. In this case, the actions of other intermediaries are unauthorized (فضوليًا) and depend on the landowner's approval; they are entitled to nothing unless the seller agrees. As for the buyer's knowledge of the original price, it is necessary if the intermediary is acting as the buyer's agent, in which case the intermediary must inform the buyer of the true price.