They do not talk to their father who married a second wife
10-3-2011 | IslamWeb
Question:
Assalamualaikum! We were living very happily. My father attempted second marriage four years back though my sister was mature. sometimes, he comes to our house. We are two brothers and two sisters. My mother and two sisters talk to him. we got angy as we had the responsibility of our elder sister and he married. Now we managed to get our elder sister married. So since that time we two brothers dont talk to our father. So is it permissible for us not to speak to our father?
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad 
is His slave and Messenger.
It is Islamically permissible for a man to marry a second wife if he is able to be just between his two wives as we clarified in Fataawa 82124 and 81469. Therefore, your father is not wrong just by marrying a second wife unless he is unjust to your mother for instance because of this marriage. In such a case he should be advised to fear Allaah and be just as Allaah Says (what means): {And you will never be able to be equal [in feeling] between wives, even if you should strive [to do so]. So do not incline completely [towards one] and leave another hanging].}[Quran 4:129]
Moreover, it is confirmed that Abu Hurayrah 
narrated that the Prophet said: “When a husband has two wives and does not treat them equally, he will come on the Day of Judgment with half of his body hanging down.” [Abu Daawood]
Besides, the father is obligated to spend on his daughter who has no money until she gets married as we clarified in Fatwa 130099. Therefore, if your father is well-off and he can spend on her but he does not do so, then he is negligent and wrong.
In fact, you did well by spending on your sister and marrying her off; this is indeed an act of kindness and goodness and verily Allaah does not waste the reward of the doers of good.
However, it should be noted that her father is her guardian, so even if he does not spend on her, it is not permissible (for you) to marry her off without his consent.
As regards deserting the father, then this is not permissible at all no matter how wrong he is; rather, it is an obligation to be kind and dutiful to him and keep ties with him in all cases, and deserting him is cutting ties with him, so you must avoid it. For more benefit, please refer to Fataawa 87856 and 85041.
Allaah Knows best.