All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
If the employee is given items to distribute to the customers of his employer [i.e. company], then he is not entitled to give them to others and he has no right to benefit from them himself or give them to his family unless he is authorized [by his employer] to do so.
Disposing of these items in other than what the employer authorized is a betrayal of the trust and an infringement to it. Allah has ordered us to preserve the trust as He Says (what means): {O you who have believed, do not betray Allah and the Messenger or betray your trusts while you know [the consequence].} [Quran 8:27]
Therefore, it is an obligation to give back the items that your father was entrusted to give to the customers, and was not authorized to take anything from them for himself, his children, or others. You may, for instance, release yourselves from the (Islamic) liability by putting them in the office of your father at his work without his knowledge, or by putting them along with other items in the company.
It is not necessary to inform the company of this. However, your father should be advised to refrain from disposing of items with which he was entrusted as he desires; he must dispose of it only in the manner which he was given permission to. He should also be told that what he is doing is impermissible.
As for the employee whom one does not know whether or not he was authorized to use those items, then there is nothing wrong in dealing with him in regard to the items which were distributed by the employer unless one knows or predominantly thinks that the employee has transgressed and has taken them without right; in which case, he should stop dealing with him regarding these items.
Allah knows best.