Is it permissible to combine a fixed wage with a percentage of the profits when working as a driver, and are monthly incentives considered part of this combination? What is the ruling on secretly taking money from the mother without the father's knowledge in exchange for driving the sister and mother? And is it permissible to combine a percentage of the work profits, a monthly allowance, and a fixed payment for transportation?

If the incentive is an essential part of the contract and the employee's salary, then there is a difference of opinion on it, with the majority prohibiting it due to the ambiguity of the wage. However, if the contract is only for a fixed salary, and the incentive is to encourage the employee or for extra work, then there is no harm in it, and it falls under the category of a commission (جعالة).

As for the matter of the mother and father, you can accept what the mother gives without informing the father, or gently refuse it. The monthly allowance from the father has no relation to the work.