Praise be to Allah.
If the situation is as you describe, then what can we say about the immense disaster of a father who does not pray or fast, who drinks intoxicants and commits immoral acts, who neglects his family and calls them to do evil deeds? Laa hawla wa laa quwwata illa Billaah; hasbunaa Allaah wa niam al-wakeel; innaa Lillaahi wa innaa ilayhi raajioon (There is no strength and no power except with Allaah; sufficient unto us is Allaah and He is the best Disposer of affairs; verily we belong to Allaah and unto Him we will return).[These are duaas recited by Muslims when faced with calamity Translator] Does he not know that Allaah says (interpretation of the meaning):
Ward off from yourselves and your families a Fire (Hell) whose fuel is men and stones, over which are appointed angels stern (and) severe, who disobey not (from executing) the Commands they receive from Allaah, but do that which they are commanded.[al-Tahreem 66:6]
Does he not know that the Prophet (peace and blessings of Allaah be upon him) said:
There is no person to whom Allaah has given responsibility and dies neglecting that responsibility, but Allaah will deny him Paradise.(Reported by Muslim, 203)
Every one of you is a shepherd and every one of you is responsible for his flock (those under his care) a man is the shepherd over the members of his household and he is responsible for them
Allaah will ask every shepherd about that for which he was responsible.(Reported by al-Tirmidhi, 1627).
There is no person to whom Allaah has given responsibility over others and he failed to take care of them by advising them sincerely, but he will never smell the fragrance of Paradise.(Reported by al-Bukhaari, 6617).
We ask Allaah to bring this man back to the truth.
Know that even though your father has caused you so much suffering, it
is not permissible for you to sever your ties with him, in spite of all that you have
mentioned. You must keep in touch with him and treat him kindly. You and your siblings
should treat him kindly and express your fears for him and your love for him, because of
his rights as a father, and because severing ties with him and ignoring him in a hostile
manner will only make matters worse. Neither you nor your siblings should obey him in sin.
You mention in your message that your father used to treat you well when you gave him
money, so if giving him money will put an end to his bad treatment and make things go back
to normal, so that you will treat one another well and he will see love and sacrifice on
your part, then why not do that? This is provided that he does not use this money to buy
haraam things. Try to restrain your anger and forget his past shortcomings in his
behaviour towards you. Try to honour him and show love towards him. Visit him and look
after him. Maybe this will stir up true fatherly feelings in him, and maybe stop him from
doing haraam things. Dont even think of severing ties with him. Get in touch with
your brother and ask him to get back in touch with his father. Know that your being
patient with him is a kind of jihaad, which will be rewarded. The idea of not visiting him
until he repents is not right, because Allaah says (interpretation of the meaning):
But if they (both) strive with you to make you join in worship with Me others that of which you have no knowledge, then obey them not, but behave with them in the world kindly, and follow the path of him who turns to Me in repentance and in obedience. Then to Me will be your return, and I shall tell you what you used to do. [Luqmaan 31:15]
Visit him, so long as it does not cause you unbearable harm or make you do wrongful things. Know that one of the ways to make a sinner repent is having someone who will call him to repent and remind him of Allaah. A child has to treat his parents honourably even if they are mushrikeen. Al-Qurtubi said:
The aayah indicates that one should honour kaafir parents as much as possible by spending on them if they are poor, by speaking kindly to them, and by calling them to Islam.
With regard to your sister, she must be careful when she stays with her immoral father. Locking herself in is a good safety measure and may well be essential at times. If she does not feel safe in the home of this immoral father, she should go and live somewhere else where she can be safe, such as in your house, if it is suitable. Maybe Allaah will give her a righteous husband who will take care of her and protect her.
We ask Allaah to guide your father and to bring him out of darkness into light. May He forgive you for your sin and help your sister and all of us to adhere steadfastly to the truth. May Allaah bless our Prophet Muhammad.