Is the father’s wife among the relatives (rahm) with whom one is obliged to uphold ties of kinship?
Question

                My father is married to someone other than my mother, and this woman has a son from another man. My father tells me and my siblings off for not asking about this woman. i.e., he wants us to speak to her, ask after her, visit her on Eid and he says that by not asking after her we are severing the ties of kinship. Is that true? Is not asking after someone regarded as severing the ties of kinship?.
Praise be to Allah.
    Honouring the father’s wife, treating her kindly and asking 
    after her are part of honouring one’s father and upholding ties of kinship 
    with him, especially since he is asking you to do that and urging and 
    encouraging you to do so. 

    The father’s wife is not one of the relatives (rahm) with 
    whom one is obliged to uphold ties of kinship, unless she is related to you 
    by blood, but not asking after her is regarded as offending the father, and 
    falling short in upholding ties with him. 

    It says in Subul al-Salaam (2/628): The scholars 
    differed as to the definition of the relatives with whom one is obliged to 
    uphold ties of kinship. It was said that they are the relatives to whom 
    marriage is forbidden. Based on this, the children of paternal and maternal 
    uncles (i.e., cousins) are not included in this. This who hold this view 
    quote as evidence the fact that it is haraam to be married to a woman and 
    her paternal aunt or maternal aunt at the same time, because that would 
    result in the severing of family ties.  

    And it was said that it applies to anyone who is connected by 
    inheritance, which is indicated by the words of the Prophet  (peace and 
    blessings of Allaah be upon him): “Then the closest to you and the next 
    closest.” 

    And it was said that it applies to anyone to whom you are 
    related, whether you would inherit from him or not. 

    Moreover, as al-Qaadi ‘Iyaad said: there are degrees of 
    upholding the ties of kinship, some of which are higher than others. The 
    least of them is not forsaking them and upholding ties by speaking, even if 
    it is only saying salaam. That varies according to ability and need, and 
    some of it is obligatory and some is mustahabb. If a person upholds the ties 
    of kinship to some extent but not fully he is not regarded as having severed 
    the ties of kinship, and if he falls short of what he is able to do and 
    should do, he is not regarded as upholding the ties of kinship. 

    Al-Qurtubi said: The ties of kinship which should be upheld 
    are general and specific. The general ties are the ties of religion which 
    must be upheld with friendship, sincerity, justice, fairness and fulfilling 
    obligatory and mustahabb rights. 

    Specific ties include, in addition to that, spending on 
    relatives, checking on them and forgiving their mistakes. End quote. 

    Conclusion: The father’s wife should be honoured and ties 
    with her upheld, and you should check on her and ask after her, based on 
    ties of religion and because upholding ties with her is part of upholding 
    ties with your father. 

    And Allaah knows best.