I have been living in Canada for the last 38 years. In north America the way of life is very different from an Islamic environment. The state laws are governing there. I understand (I study a lot of Quran tafseer and hanafi fiqh) what the Islamic laws are and how they are to be applied in an Islamic society. But how they could be applied to our lives in north America, for instance:
1. in Canada husband and wife are joint owners of all assets, means all wealth regardless of the fact the wife works or not. I worked all my life and made 3 to 4 times more than my husband. In a way, my husband never supported me. In the view of the Islamic Shariah how the laws of inheritance should work? In the light of the state law which dictates that after one's spouse is dead, the surviving spouse gets 100% .
2. We have a son and a daughter. In case of our (both) death, how the wealth should be distributed? State law dictates 50 -50% to each. One of your reading says that in our lives we can give whatever we want, which is Hubba. Please explain in details.
In principle, when you are living in a country you need to follow the rules of that country. This is because as a resident of that country you have entered into a covenant with the ruling system to follow the rules and as you know breaking covenant is a serious sin in Islam.
There can now be two cases:
1. Some of the rules of the country stop you from practising some of the essential parts of your religion. For instance imagine a country where there is a rule that Muslims should not pray or that every one needs to experience fornication before marriage.
In this case a Muslim needs to do all that he can do migrate from such place.
As far as I know there are no countries with rules like the above.
2. Some of the rules of your country of residence (that is a non-Muslim country) do not allow you to follow some of the rules of the Sharia.
In my view, in this case the rules of the country of residence prevails for the reason that I explained at the start of this post. In fact those rules of Sharia that require the state to carry them out (like the penal law) can only be observed in a Muslim country where the state is taking that responsibility.
Of course the minority Muslims can try to convince the state to allow them follow their own Sharia.
To be more specific about your enquiry:
Of course in both cases that you referred to (husband or wife or both dying) the rules of the inheritance according to the Islamic Sharia will be different from what you described as the state rule. Again, if it is possible that Muslims appeal to the state to allow them apply their religious rule in these cases that will be the best solution. I am however aware that this in most cases cannot take place. As I stated earlier, in these cases the state rule needs to be observed.
The rules of inheritance that are described in detail in the Qur'an apply only to the wealth that remains after carrying out the will and paying any debts. This is the clear instruction of the Qur'an (4:11, 12). Therefore a person can write his will the way he deems it to be appropriate.