Sheikh `Abd al-Wahhâb al-Turayrî, former professor at al-Imâm University in Riyadh
The distribution of the estate cannot be decisively determined before death takes place. The reason for this is because the inheritors might change. However, I will inform you of the way your estate should be distributed should those inheritors remain exactly as they are today.
The division will be as follows:
1. Your wife receives 1/4 of the estate if you do not have children from her or from another woman. If you have children, this percentage will change.
2. Your wife’s daughter from a previous marriage receives nothing from your estate unless you choose to make a bequest to her.
3. Your mother receives 1/3.
4. Your sister, if she is your full sister or a half sister from your father’s side, receives 1/2 of the estate. If she is a maternal half sister, the case will be different. We can only reply to you after you explain her position.
5. Your deceased brother is not entitled to anything.
6. Your sister-in-law is not entitled to anything.
How to carry out the division:
Since the shares 1/3, 1/4, and 1/2 total up to 13/12 an therefore exceed the total estate, everyone's shares will be reduced and the estate will be divided into 13 shares.
Your wife will receive 3 of the 13 shares.
The mother will receive 4 of the 13 shares.
Your sister will receive 6 of the 13 shares.
If you wish your stepdaughter (or some other person) to receive something, you may leave her a bequest. A person has a right to alot up to one-third of his total estate as bequests to non-inheritors. The bequests are to be distributed before the division of the inheritance described above.
Source: Islam Today