Praise be to Allah.
What we think you should do with regard to this serious problem, is advise your father in a wise and gentle manner, and explain to him how bad this behaviour is, and tell him about the consequences of what he is doing and saying, and the trouble that has befallen you because of it, and the harm and upset that has befallen the people around you. You should explain to him the danger of not controlling one’s tongue, for undoubtedly he must have some awareness of that.
You should try to advise him in a wise and gentle manner, such as bringing some da‘wah material and books which speak about the sins of malicious gossip, backbiting and spying on others, and warn against such things. You can leave them in the house where he will see them, in the hope that he will look at them and will follow what is mentioned in them. Or you can sometimes invite people to the house whom your father respects, such as the imam of the mosque where he prays, or some of his friends, and in the course of their conversation they can explain how abhorrent it is to spy on people and backbite about them, and how dangerous that is.
If possible, you can distract your father with something beneficial that he can focus on – such as books and magazines, or some worldly or commercial work, and other things that will benefit him and also distract him from focusing on gossip.
We understand what you are suffering from by having to deal with these (negative) characteristics and the problems that result from them, but we do not think that there is any practical way of dealing with your father apart from trying to communicate with him and striving to reduce the impact of these negative characteristics that you described in your father, and trying to reduce the impact that they have on the people around you, and trying to make amends, by apologizing to the neighbours if they are affected by his behaviour in any way.
Seek the help of Allah to deal with the problems that have befallen you; be patient and offer a lot of supplication for your father, asking that he be reformed and mend his ways, and that he be protected from the evil of his own self and that the people around him be protected from the evil of his tongue and the negative consequences of his actions.
It should be pointed out that what your father is doing does not mean that he is not deserving of honour and kind treatment.
One of the greatest ways of honouring him is offering supplication for him, asking that Allah, may He be exalted, turn to him in mercy and cause him to repent sincerely from what he is doing, and that Allah, may He be exalted, forgive him.
Allah, may He be exalted, says (interpretation of the meaning):
“and say, My Lord, have mercy upon them as they brought me up [when I was] small”
Ibn Katheer (may Allah have mercy on him) said:
“and say, My Lord, have mercy upon them” that is, when they grow old and when they die.
End quote from Tafseer Ibn Katheer (5/64).
It was narrated from Abu Hurayrah that the Prophet (blessings and peace of Allah be upon him) said: “A man will be raised in status in Paradise and will say, Where did this come from? And it will be said: From your son’s praying for forgiveness for you.” Narrated by Ibn Maajah (3660); classed as hasan by al-Albaani in Silsilat al-Ahaadeeth as-Saheehah (4/129).
We ask Allah the Almighty to relieve your distress and guide your father.
And Allah knows best.