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.
Dear brother, thank you for your question and for your commitment to the rulings of the Shari`ah concerning inheritance.
As for your query, giving children any of a parent’s property while being alive should be equally done.
It is totally different after death, as that must be according the inheritance laws of the Shari`ah. A boy get twice as much as a girl and girls get equal shares regardless of being married or not.
Responding to your question, Prof. Dr. Monzer Kahf, Professor of Islamic Finance and Economics at Qatar Faculty of Islamic Studies, states:,
In giving gifts during one’s life time, a parent should give his/her children equal shares regardless of their gender or their being married or not. It should be the same for boys and girls and no difference between married or single sons and daughters.
But, in inheritance, it is to be distributed after death. A boy gets twice as much as a girl also regardless of being married or not.
Another issue may be related to this. If a parent spent on the marriage of a child, and there are other children not married yet, he/she should also spend on their marriage in a similar way.
Parents cannot make this in their last will because it will affect the obligatory shares. I believe that one must make a gift to the unmarried equivalent to what she/he spent on the marriage of others.
Allah Almighty knows best.