Reply from Agony Uncle
Your step mother and your brother form your father's presumable second marriage are your father's dependant. Whilst he is alive there is no need for you to maintain them.
Your father has a duty to provide for them if he makes a will in a unfortunate even of your father's demise. They will inherit what is stated in the will. In the absence of a will accureling to the law on intestate succession ie succession without a will your step mother will get half of your father’s estate whilst you and the new sliding together with other siblings will got the maiming 50% in equal shares.