Distribution of assets of the deceased

I have a question on the sharia distribution of assets of the deceased.

My brother passed away recently. He was married to a widow who had four children from a previous marriage. He had no children of his own. His nikah was not registered in terms of SA law. His mother is still alive and we are four surviving brothers. There are certain monies due from his provident fund and insurance. We were called to a meeting at which the distribution was discussed. I would like to know in terms of Sharia how the distribution is to be done.