If the case goes like this that your father died and he married twice. He had two daughters (you and your sister) and one son from his first wife. Then your mother died. And your father married second time. You have a sister from his second marriage and still your stepmother is alive. In this case, the inheritance of your deceased father shall be divided into 40 shares, out of which your stepmother shall get five shares, your brother 14 shares and the sisters will have 7-7 shares (including step and real).
Wife: 1×5= 05
Son: 1×14= 14
Daughter: 3×7= 21
Total: 40 Shares
Note: If the case is different, explain it and submit the question again.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband