Answer
Wa `alaykum as-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
As for the will, it is allowed for the baby but not for any of the heirs. The whole estate is to be divided into three equal thirds; the first to the two full sisters and the other two for you and your sisters.
Responding to your question, Prof. Dr. Monzer Kahf, Professor of Islamic Finance and Economics at Qatar Faculty of Islamic Studies, states:
As the case is described and as the mortgage debt is on the deceased (your mother, may Allah have mercy on her) you should start with the payment of funeral expenses, then the mortgage debt. Then the will (wasiyyah), which is valid for the baby because he is not an heir, is not valid for your sister because she inherits as an heir although she has mental problem. Of course, this wasiyyah must not exceed one third of the estate after expenses and mortgage debt.
The balance after paying these three items is divided into three equal parts; one third goes to the two full sisters to be divided equally between them and the two thirds is to be divided between the three of you; daughters of the deceased, also equally between you. Other siblings of the deceased are all blocked by the presence of the two full sisters.
Please, remember that this distribution is mandatory as it is simply an application of verses of Surat An-Nisa’ (4:11-14). Please, read especially verses 13 and 14 of the same Surah and realizes how strong their obligation is.
Allah Almighty knows best.
Editor’s note: This fatwa is from Ask the Scholar’s archive and was originally published at an earlier date.