Are the commissions a an engineer receives from factories, in exchange for recommending their equipment to a supply company, considered unlawful (haram), knowing that he also receives a percentage of the profits from the supply company, and that these commissions may increase the price of the equipment for the supply company, and he has not informed the factories that this percentage is a commission for him?

If your work involves brokerage for the buyer, there is no harm in taking a commission from the seller without the buyer's knowledge.

However, if you are an agent for the buyer, it is not permissible for you to take a commission from the seller except with the buyer's knowledge and consent.

If your taking of commissions involves deceiving and defrauding factories, by making them believe something untrue in order to obtain the commission, then it is not permissible for you to take those commissions. You must absolve yourself of this by returning them to their owners or seeking their forgiveness.