Providing for one's father's new wife and her children

My father has married a young woman who has brought three young children with her and a grandson. My father does not work and he is almost seventy now. He has no pension whatsoever and his only source of income is the money me and my siblings give him. This is his third marriage. The first was to mother who passed away, he got divorced in the second marriage and he was living with my elder sister until now. Then he got married and decided to move into the unfinished house we were building for him. The question is, me and my siblings do not have well paying jobs and still we tried our best to care for him but now he has brought a woman and 4 children that will need support from him. As a Muslim, is it my duty to care for his family? It was already hard to care for him alone and just how are we going to manage taking care of 6 people including him and his wife? Will Allah Ta'ala be angry with us? Because when we send him money now its never enough and we also have our own lives to care for.