Me and my wife had a verbal agreement that if i should pass away she becomes the owner of all what is left behind and vice versa, now that she passed away i am left with the little belongings etc and i would like to know if i am the sole owner of it.
There are no children in this marraige.
Does her sister or family members can make any claim of her belongings ?
In principle, a bequest made in favour of an heir is not valid. The arrangement described in your query is not permissible as it results in making a bequest in favour of an heir. Rasulullah (Sallallahu Alahi Wasallam) has prohibited making a bequest in favour of an heir and ruled that such bequests are invalid (Tirmizi). In this case, you are an heir to your wife and the bequest that she made that all her belongings should go to you is invalid. A bequest in favour of an heir will only be valid if all the heirs agree to it without coercion after the demise of the testator/testatrix.
You will be one of her heirs. Her family members also inherit from her. You will have to provide a list of her heirs for us to give you a breakdown on how the estate should be distributed.
And Allah Knows Best
Jamiatul Ulama (KZN) Fatwa Department