It is not permissible for your father to accept what is given to him because of his work
Question

My father works for a company and some people give him money or personal gifts at work. He stopped taking this money but he soon went back to taking it. He tells me, “I don’t differentiate between those who give me gifts and those who do not.” What is the situation with regard to the money we take from him, the food we eat and the clothes and gold we wear; and what is the situation with regard to our du’aa’ to Allaah. When he gives us food as a gift, should we accept it? Once he forced me to accept clothes from some of these people. Is it permissible for me to wear them?.
Praise be to Allah.It is not permissible for your father to accept what is given to him because of his work, because al-Bukhaari (6636) and Muslim (1832) narrated from Abu Humayd al-Saa’idi that the Messenger of Allaah (peace and blessings of Allaah be upon him) appointed a man to collect the zakaah, and when he had finished his work, the man came and said, “O Messenger of Allaah, this is for you and this was given to me as a gift.” He said, “Why don’t you sit in the house of your father and mother and see whether you get any gifts or not?” Then the Messenger of Allaah (peace and blessings of Allaah be upon him) stood up after ‘Isha’ prayer, testified (to the Oneness of Allaah) and praised Him as He deserves to be praised, then he said, “What is the matter with a zakaah-collector whom we appoint, then he comes and says, ‘This is for you, and this was given to me as a gift.’ Why does he not sit in the house of his father and mother and see whether he receives any gifts or not? By the One in Whose hand is my soul, no one of you steals anything from it [the zakaah] but he will come on the Day of Resurrection carrying it on his shoulders, even if it is a camel that he brings groaning, or a cow that he brings mooing, or a sheep that he brings bleating. I have conveyed the message.” Abu Humayd said: Then the Messenger of Allaah (peace and blessings of Allaah be upon him) raised his hand until I could see the whiteness of his armpit. 
So your father should be told what the Messenger of Allaah (peace and blessings of Allaah be upon him) said: “ ‘Why don’t you sit in the house of your father and mother and see whether you receive any gifts or not?’ – because you are only getting these gifts because of the job to which you have been appointed.” 
If that is the case, then these gifts belong to the job, and he has no right to take them for himself. 
Shaykh Ibn Baaz (may Allaah have mercy on him) said: This hadeeth indicates that it is obligatory for the person who is employed by the state to do the job for which he has been appointed, and he has no right to take any gift that has to do with his work. If he takes it then he should put it in the bayt al-maal (public treasury), and it is not permissible for him to take it for himself because of this saheeh hadeeth, and because that is a means that leads to evil and betraying trust. 
From Fataawa ‘Ulama’ al-Balad al-Haraam, p. 655 
Ahmad and al-Bayhaqi narrated that the Prophet (peace and blessings of Allaah be upon him) said: “Gifts given to workers (employees) are ghulool (lit. stolen war booty)” i.e., a betrayal. This hadeeth was classed as saheeh by al-Albaani in Saheeh al-Jaami’, no. 7021. 
Your father’s saying that he does not differentiate between those who give him things and those who do not does not alter the fact that this is haraam, but if he makes things difficult those who do not give him anything, then that makes his sin more serious. 
His claim that he does not differentiate between those who give him gifts and those who do not is dubious, because gifts have an effect on the heart. Man is created in such a way that he likes those who are kind to him, so these gifts may make your father biased towards the one who gave him the gift, so he may give him something he is not entitled to. So let him fear Allaah, and refrain from these haraam earnings, for all the pleasures of this world are temporary, so how about if they are also haraam? 
Whatever he has received of these gifts, it is not permissible for you to take them or make use of them, because this is haraam wealth, 
Whatever you have saved from your father’s salary that he was paid in return for his permissible work, there is nothing wrong with you benefitting from it. 
With regard to the clothes that he forced you to take, if they were bought for the regular price, there is nothing wrong with you wearing them, but if he took them as a gift or for a reduced price, you should not wear them. Try to advise your father, and remind him of the seriousness of haraam wealth, and encourage him to ask the scholars so that they can dispel his doubts. 
And Allaah knows best.