Is it permissible to record sums of money paid to consulting engineers or employees of other companies in the accounts, knowing that these are paid to avoid harm or obstruction of work, and is the salary received from this entity unlawful?

As long as the brother's work in accounting at a contracting and maintenance company does not involve assisting in something forbidden, it is permissible. And if employees are forced to pay a bribe to obtain their rights and avert injustice from themselves, then it is permissible for them; because what is given to obtain a right or avert injustice does not fall under the forbidden bribe.